Pioneers in Science and Technology Series: Clarence Larson

PIONEERS IN SCIENCE AND TECHNOLOGY SERIES
ORAL HISTORY OF CLARENCE LARSON
Interviewed and Filmed by Jane Larson
Date Unknown
Transcribed by Jordan Reed
MR. LARSON: My name is Clarence Larson and I am director of the Pioneers of Science and Technology video tape project. The first part of this is an experiment which I am going to give some of my biographical information starting essentially from the time I was born in 1909 in the town of Cloquet, Minnesota, which is in the northern part of the state near Lake Superior.
My earliest recollection of any happenings and many psychologists and students of child psychology will dispute this is a vague recollection of my mother taking me in her arms outside and pointing to something which was a light. And vaguely in later years I tended to associate that with the appearance of Halley’s Comet in 1910. Theoretically, this was too young for any such memory to exist, but I just recite this as an interesting background because now, next year, we are faced with the return of Halley’s Comet. My early childhood was really quite uneventful. Our town was a homogeneous town primarily devoted to lumber manufacture and paper manufacture and slightly later it was devoted somewhat to the manufacture of insulation. In fact I believe the first manufactured insulation was made of fiber wood which was placed between two sandwiches which gave an insulating property for the insulation of houses.
My first recollection of a big event in my life was the so-called Big Fire of 1918. The fall of 1918 which incidentally was the last of World War I, was a very, very dry summer and the woods were tender dry. Of course that brings on the possibility of very serious forest fires because at that time Minnesota was a lush grove of timber. Surely enough, a large forest fire broke out and within a day, our town was endangered. When we saw the fire coming and we had also heard reports from the train crews coming through, of the serious fires down below us, where by a town of about 500 was completely wiped out with grave loss of life. As the fire approached our town, all of us were able to escape due to the foresight of a train dispatcher, who held all of the trains coming through including boxcars, coal cars, passenger trains, any form of transportation that was available was held so that we could evacuate the entire town of 10,000 within a few hours. I doubt even with our modern planning and everything that you could have arranged such an efficient evacuation with no loss of life during that short period of time. At the time, I was nine years old, and of course, to this day, I have a vivid recollection of the tremendous wind storm which was the characteristic of the fire storm, the wind being actually generated by the tremendous fires that were, that broke out.
[Break in video]
MR. LARSON: As you can readily see, this was a very traumatic time with the entire town being evacuated and sent to Duluth and Superior over the rails. At that time there were practically no automobiles in existence in our home town. Perhaps maybe five or six automobiles were in existence. Roads were very poor, one and a half lane roads between Cloquet and Duluth. Unfortunately, those people who did try to get away by car were burned to death because they were caught on the road by the fires. So fortunately, practically the whole town was saved by being evacuated to Duluth and Superior. Temporarily, we were brought to centers, school gymnasiums, civic centers and places like that. The people of Duluth and Superior were mobilized and took them, took each one of the, families who volunteered, took one family from Cloquet and so we were temporarily quartered in people’s homes in Duluth and Superior, an outpouring of real generosity on the part of the people. I will never forget the cordial reception we had from the people of Superior, Wisconsin. Well, following that, to make a long story short, we did rebuild the city of Cloquet. At first we lived in temporary housing and then build a permanent house, which stands to this day and which I have visited just last year.
Following that, it was about time for me to go to high school and there was nothing particularly outstanding in high school. Before I went to high school, I had the opportunity to participate in an educational experiment. We hear of all kinds of educational experiments today, and this was no exception. They gave all of us a test in the sixth grade, and if we scored high enough, there were I think 25 of us selected to go into a special class which would study both seventh and eighth grade subjects together. This included math and, of course, it was advanced arithmetic, and algebra, literature, writing and some history and most notably, great emphasis was put on spelling. At the end of that time, it was time to give us examinations, and these examinations were not trivial. The examinations, from the seventh grade on through the finish of high school at that time, were conducted by the state education department so that in order for us to go into high school, we were forced to take state generated tests in both seventh and eighth grade subjects and pass both of them in order to receive credit. As a result of this experiment, four of us passed into high school and the rest of them had some deficiencies which they had to make up before they could be full term freshman. But four of us made it into the regular high school classes and therefore I was one year ahead. As a result when I went to, went into my senior year, I was 15 starting my senior year. So I graduated quite early.
During, particularly my freshman and sophomore year and perhaps even in the eighth grade, I became very interested in electricity and I read every book in the library on the subject and decided to perform some experiments. So we rigged up a little telegraph line between my home and some of my friends and neighbors and we were able to communicate back and forth through these lines. We made the telegraph ourselves, [inaudible] coils. In order to get the battery power, we scrounged around the Bell telephone discard pile and they used to use batteries in the phones in those days. The used batteries had enough electricity, electric power, energy left in them so that we could use them in this purpose by connecting them in series and parallel. So we had a great deal of fun with this and then shortly after I became interested in wireless, and at that particular time, in 1920 and ’21, it was actually before the days of broadcasting. I believe broadcasting started around 1921 and as a generator of radio frequency signals we used the, a spark gap. My source of a spark gap was a Ford spark coil which I connected to the batteries and generated about a half inch spark, connected that to an antenna and we were able to actually signal as far away as about one and a half miles using this set up. So I became interested in electronics and electricity at a very early age.
During my high school years, strangely enough I had not really intended to go away to college. Remember this was back in 1924, 1925 and ’26, and in our hometown a very small percentage of the graduates went on to college. I did not expect actually to do so. In spite of the fact that I got reasonably good grades, I was not at that top of my class or anything. So I decided after I graduated that I would attempt to get some sort of a job and then work up from there. Most people, my brothers had both obtained jobs at the lumber and paper companies there in town and I thought I would follow along the same path.
However, I was given the opportunity to do boys work at the local YMCA and strangely enough I was offered for those days, quite a handsome salary in order to do this. So as a 16-year-old, I became a full time employee as assistant YMCA secretary for boys work. I got this particular job because I was actually very interested in the Bible at that time. In fact, I read considerably and I was active in the youth groups in the church and so on. Although I never thought about it particularly, I suppose that was why I happened to get this job. Well as a result of this, I was given the opportunity to participate in organizing boys’ tournaments in basketball and soccer and tennis, all kinds of activities of this type. Also occasionally since the YMCA was religion-oriented I was called upon occasionally to serve as a substitute minister in some of the small churches in the rural communities. So, I would occasionally go out and give the service and the sermon of that time. As a matter of fact, I think I still could today give the sermon which I gave at that time, which was my favorite one with the title of, taken from the Bible, and Jacob’s Well Was There, has the theme, of course, that the fact that Jacob had done some very fine work in drilling that well, digging that well. People for generations afterwards benefitted from the work that he did during his lifetime. So I think there was a very fine moral lesson to that and it was, as I say, I can still remember that particular sermon that I gave.
Well, as time went on and I read more and more I became more interested in the possibility of going to college and of course actually probably as soon as I started the job I began to think, perhaps if I saved my money I would be able to actually go away and get an education in college. So I saved a reasonable amount of money and with some trepidation, decided to quit my job, which incidentally by that time was paying for those days an enormous salary. I believe it was $125 a month, which was a very good salary and enrolled at the university and took the usual courses. I had become interested in chemistry. So I thought that I would end up as a chemistry teacher after I graduated from college, but as I grew more and more interested as I went through college, I decided that if I could I would go on to graduate work, or perhaps work in industry. I grew less and less interested in education courses. As a matter of fact I became very bored with the education courses and did not like them at all compared to the scientific, mathematical, and technical courses that I took. So, as a, to make a long story short again, I graduated in the depth of the Depression. This was 1932 and not a member of my graduating class in chemistry received a job offer, with the exception of one man who got on offer from his uncle who owned a small chemical plant.
So, I was fortunate in getting a fellowship at the University of California and decided to move to California. My mother was quite tearful about this, moving so far away, but I really enjoyed the challenge and looked forward to it and journeyed to California where I did my graduate work. This was in 1932 and as I lived through those graduate years, I did not realize what a revolution in science was beginning to occur right around me. The, it was at that time, actually in 1932 that E.L. Lawrence invented the cyclotron and of course I naturally was conscious of it, but I did not have the full realization of the revolution that that made in physics. My work of course was in chemistry and my, some of my work that I did, involved the physical chemical properties of biologically important compounds. As a result, I studied the electrochemistry of these compounds; its behavior in electric fields determined the electrode potentials of various systems and had learned a great deal in addition to chemistry, learned a great deal about electrochemistry which was to serve me in good stead later on. Well to again, make a long story short, I was, I finally received my Ph.D. and by that time, of course, there were two avenues open to me. One I could go into research work and the other I would go into teaching.
As a matter of fact, I received a full time research assistantship at the Mount Zion Research Foundation almost coincident with finishing up my thesis work for my Ph.D. degree. So I did research work for a year and learned about an opportunity for an instructorship at the College of the Pacific at that time. I was very pleased to do this because I actually felt college teaching would be an ideal life. You could do some research work and also, I always did enjoy teaching, particularly at the elementary college level. So I did obtain the position. I found out later that there were actually 100 applicants for this position. I didn’t realize at the time how lucky I was to actually obtain the position. I found out later when I became head of the department that those applications were on file. So I glanced through them and I must say that I never could quite figure out why they hired me rather than some of the very well qualified people that they had. At any rate I was very happy to obtain the position and my years of teaching there at the college were very happy years. I think that the combination of a small liberal arts college together with small classes forms an ideal situation. In addition to that, I did have a little opportunity to do some research work and since my work in graduate school brought me into touch with the marvelous developments going on in the field of, the development of artificial radioactivity, the application of the cyclotron to radioactivity.
I did not actually participate in that because I was so busy trying to iron out my own research, but I can remember distinctly one, attending a lecture given by Dr. John Lawrence, the brother of E.L. Lawrence in which he demonstrated the radio, the absorption of radioactive tracers. They had produced some radioactive sodium in the cyclotron, dissolved it in water and mixed it with perhaps some lemonade or something. They had as a demonstration, they had one of the workers there drink the radioactive sodium which is in the form of radioactive chloride. They had a Geiger counter on the finger which was extended away from the Geiger counter and perhaps, within about two or three minutes, the Geiger counter began to click from the radioactive sodium which was absorbed into the blood stream and then circulated all the way to the fingertips. It was a very interesting demonstration of the use of tracers in biology. Well as a result of some of this, I made casual acquaintance with E.O. Lawrence and some others on the staff. I was able to get some radioactive tracer material by taking the targets which held their main experiments and there was always a little stray radiation hitting the targets. I was able to get the targets which contained radioactive iron, and cobalt, and manganese and I was I able then to do elementary experiments in the use of radioactive tracers involving iron, chromium, and manganese. At that time I used the Lauritsen Electroscope instead of the Geiger counter because the Geiger counter was still in the very elementary stages. But the Lauritsen Electroscope, which was a modification of the gold leaf electroscope that Madame Curie had used way back in about 1905, and this was a special one with an optical scale back in it, which made the readings easier, but the principle was actually the same. I have spoken to Dr. Glenn Seaborg and he used the Lauritsen. More recently I have talked to Phil Abelson and he used the Lauritsen electroscope. So these very simple, cheap devices can be used for very fine research work. One of the things that I tried to do at that time was to use the radioactive tracer chromium as an analytical tool for the determination of sulfate in very low concentrations. This, I was unable to do satisfactorily because of the very low level of chromium activity that I was able to get. Over 15 years later when radioactive chromium became available I did go into the laboratory when I was director of the Oak Ridge National Laboratory and finish up that experiment and actually published the results using chromium as a method for determination of the sulfates. It was sort of a trivial thing, but I did this more or less to satisfy my ego perhaps.
Well at any rate, as a result of this experiment that I was doing at the College of the Pacific and I did have some very fine students there, and I enjoyed the work very well, very much, but historical events did overtake us. I can remember distinctly, of course, one of the things beginning in about 1938 was the peace movement on the campuses of all of the colleges in the country. Our particular college was no different. We had a very powerful peace movement. The students were very enthusiastic about it at the time; of course Hitler was becoming more and more powerful, more and more threatening. You could see the war clouds gathering in Europe and this was, alarmed everyone and everyone was very anxious to preserve peace. But of course, those of us who had studied history could see that the peace movements were not going to be able to stop Hitler. At any rate, I can distinctly remember the leader of the peace movement who happened to be one of the students that I served as an advisor. Each one of us were assigned a certain number of students to advise on courses and sign approvals to take courses and so on, and he explained with great earnestness the demonstration that they were organizing, this was in 1938, as to the world wide peace movement. It was actually to be held at this football stadium there at the college. They had one of the high bishops of the church to serve as the main speaker and the students were all organized to give demonstrations with banners and so forth against war. It was a marvelous demonstration that they put on. It was very sad therefore, that just a few years later, as, within a course of a few months, war broke out in Europe and then later on, of course, we did have the bombing of Pearl Harbor. Oddly enough those students who were so active and so earnest in the peace movement overnight became very patriotic and were the first ones to volunteer to fight for our country. So I think there is a very good illustration about how history repeats itself because in England we had the same thing happen. I can remember talking to some people who had equivalent experience with the earnest students who were in the peace movement at Oxford and Cambridge, were among the first to volunteer for flying in the RAF and were perhaps the leaders in the great fight in the Battle of Britain. But to come back to as soon as the war broke out, things were changed entirely. The college was converted very much to preliminary training for the Air Force which was being expanded at the time and we were all asked to beef up our courses. I taught modified math courses for students going into the Air Force and, as I say, things were beginning to completely change around.
Actually a few years earlier, in my classes, there was an event which took place which was very significant. I believe it was in early 1939 that we had our courses in chemistry and one of our most popular activities was a Monday afternoon seminar in which we would take one given topic and assign it to a student and he would read up on it and then report on recent advances. Then we would cover all of the topics of immediate interest in the field of chemistry. This one day, there came out this report from Germany about the work of [Otto] Hahn and [Fritz] Strassman on the discovery that with the absorption of neutrons that uranium was split approximately in half giving rise to radioisotopes. This was a nuclear reaction which had not even been dreamed of, which had never occurred to people that it could possibly be. In fact the neutrons had been used to bombard uranium in many of the most prominent laboratories of the world: Fermi in Rome, the Curies in Paris, Hahn and Strassman in Germany, and in the United States there were several laboratories. All of them bombarded uranium, but none of them recognized the fact that in a large number of the hits of uranium, of neutrons on uranium, that there was a splitting of the atom. Almost all of them thought that the uranium was absorbing the neutron and becoming instead of uranium-238 it would become uranium-239 which would actually become then a transuranic. In fact, Fermi had postulated the existence of several isotopes of elements 93 and perhaps 94. By mistake he had actually been awarded the Nobel Prize in physics, I believe it was in 1937 or 1938, because of a mistaken diagnosis of what was happening. Of course, his tremendous work in the field of physics and then actually his methods, the development of the methods that he used full, he fully deserved the Nobel Prize for many other things besides that, but it was really interesting that he was mistaken in his interpretation. Well, as soon as that was published, in our little group of our chemistry seminars, we had some sort of a topic involved with something like ion exchange resins which were beginning to be made at that time. We discarded that topic and we discussed the implications of the splitting of the atom, whereas people had postulated that they could tap the energy of the atom eventually and give us an unlimited supply. This was the first time that we were actually able to postulate a practical way in which the energy of the atom could be tapped.
Well, later on, we find that, I found that when the war broke out, as things changed, and I received a call from Berkeley to come down and be interviewed for some new project that was being mobilized there. E.O. Lawrence was mounting this very secret project. In fact I really didn’t know what I was being called down there for until I actually joined the project. During the interview, I was given no hint what-so-ever as to what the project was. There was only that the project was extremely important and that it would be vital to the war effort and that my particular work would fit in very well to the project. So I decided to resign, or take a leave of absence in 1942 and join the project at the University of California.
[Break in video]
MR. LARSON: All right. Well now, with regard to joining the project at Berkeley, my first job there after receiving some slight indoctrination, at which time I was told what the project was. I can remember very distinctly in talking to E.O. Lawrence about the time schedule. He said it is absolutely necessary that the project be finished by July 1945 and it would be necessary to have roughly 100 kilograms of the product produced by that particular time. Now, this doesn’t seem like very much, but this was in July of 1942 and the process by which this U-235 was to be produced was the electromagnetic process which essentially was a large mass spectrograph in which the atoms of uranium were vaporized, ionized in an arc, accelerated and then bent in a magnetic field and at the end of 180 degrees travel would be collected in two separate small boxes, one containing, in theory, the U-235 and the other box the U-238. At the time, I joined the project in 1942, there had been produced somewhat on the order of a milligram or two of the U-235 fraction. So you can see there was a long way to go in order to get this produced.
Well, my first job was to distill the uranium tetrachloride which was the charge material for this process and to distill it and sublime it in a pure form so that it then could be used to, put in the source to be ionized. This was no mean job because it involved distilling under high vacuum and under carefully controlled temperature conditions and it was a very difficult process. It had to be done under absolutely vacuum tight preparation for the actual distillation and following that the unloading had to be done inside a dry box to avoid any possibility of moisture because moisture hydrolyzed the highly hydroscopic UCL-4 and then would destroy its usefulness. Well, we managed to get enough of this prepared and actually worked out a method for preparing it on reasonably large scale. So my next project was to turn our attention to methods for recycling the uranium in the process. It turns out that whereas the process sounds very simple, in practice, it’s not very simple. Uranium tetrachloride is vaporized and then is ionized in an arc and then led into the collectors containing, theoretically, the U-235 or the U-238. Unfortunately the ionization is very, very incomplete and so only five to ten percent of the uranium which is vaporized gets into the ionic stream and then the rest of it collects on the walls of the containers. So that had to be washed down thoroughly and collected because uranium was very valuable and then it had to be precipitated, recovered as uranium oxide and then converted to uranium tetrachloride, purified again and then go through the whole cycle again. So this got to be very complicated and there was a great premium on getting as high a recovery as possible because uranium was reasonably scarce, at least there was none to be wasted and therefore this had to be done with great care.
Well, we worked out a passable method for doing this and the recycling turned out to be practical. We did some of these experiments in the 37-inch cyclotron at Berkeley and tested our methods for recovery and worked it out on a small cyclotron which was converted into a mass spectrograph and we had a good research tool to carry out all of our experiments. Well this went on and the method which was being used was not all that satisfactory because in theory if you have pure uranium salts this works out very well, but uranium tetrachloride is a very corrosive material and any metal that it comes in contact with is immediately corroded and actually dissolves the iron and the steel. If there is stainless steel, it would dissolve some of the chromium off. If there are nickel parts, it would dissolve some of the nickel, so in general you ended up with a small amount of uranium of and a large amount of impurities to be recycled. This complicated the actual process considerably, in fact, lead to great difficulty as we will see a little later in the actual process. While this was going on, it seemed to me that the ideal thing to do instead of trying to separate out by certain agents the iron, chromium, nickel, and all the rest of these things and then leaving the uranium in solution that it would be much better to do it the other way around, precipitate out the uranium and then leave the rest of the things in solution. This was a good idea, but there was no agent known which would precipitate out uranium away from everything else, except one agent which is hydrogen peroxide. It turns out that uranium is precipitated by hydrogen peroxide to form uranium peroxide almost quantitatively under the right conditions and so it seemed that we had actually discovered the best possible way to do this. One complication however was that peroxide is very unstable in the presence of certain metals, particularly iron. In fact, iron actually decomposes the peroxide catalytically. For those of you who remember the early days of medicine, we used hydrogen peroxide to sterilize cuts and you had the impression that the hydrogen peroxide was working because it bubbled and fizzed. Actually this was because of the presence of certain enzymes in the blood and perhaps some iron which decomposes peroxide immediately. So in our so solutions, we had a lot of iron in them, there was no possibility of using this reaction because the iron catalytically decomposed the peroxide. This puzzled me a lot and I decided to eliminate the iron by complexing it with certain agents. There were complexing agents which would tie up the iron and make it unavailable for catalytic purposes and this, there was such a variety, I could, some of which are even used today in certain processes, but the net effect was they were all very expensive, all very scarce, and they didn’t work too well anyhow. So I finally had to abandon that approach and it was assumed that we really couldn’t do it until I hit on an idea which was probably a throwback to some of the research work that I did at one time. In my research work on biological compounds, I found that many of the organic compounds were unstable particularly if heated slightly. Even in some solutions they were unstable and so we had to keep them cooled. Many of these reactions where you separate important compounds of this type have to be carried out either in a refrigerated atmosphere, or carried out in such a way, so fast that you don’t, you didn’t get a chance to get this decomposition. So I tried the simple expedient of refrigerating the solutions and much to my amazement, the problem was solved almost immediately. If you kept the solution refrigerated, there was no decomposition. So therefore, at once, we had a possibility of precipitating the uranium out in very pure form, away from all of the other elements of the periodic table, because it was specific, peroxide precipitation was thought to be specific only for uranium. Well this was a little too good to be true. Actually it turned out later that the rare earths are also precipitated by peroxide and other things such as many of the transuranics, but since we didn’t have transuranics at that time, we didn’t have to worry about them. So for all practical purposes uranium peroxide precipitation was very specific and it worked for this particular purpose.
[Break in video]
MR. LARSON: The question then arose as to what are the quantitative relationships which will enable us to actually optimize the completeness of precipitation of the uranium peroxide and the variables, of course, are hydrogen ion or pH, the other variable is the concentration of the peroxide. There is a mathematical relationship between those called the equilibrium constant and I decided to determine the value of this so that we could use this in our calculations. With a simple series of test tube experiments, I worked out, by using I think about 20 test tubes and observing the effect in each one, to be able to zero in on the approximate values of the pH and the hydrogen peroxide concentration and then develop a mathematical relationship which enabled us to calculate over broadened number of conditions and we were able then to optimize the process for the proper conditions. A few years later, the equilibrium constant was determined with great accuracy and it turned out to be within one percent of that value that I determined by that rough method during a period of one day. So now we were essentially ready with the basic experiments and we were then ready to go to Oak Ridge.
Oak Ridge in the meantime had been selected as the actual locality for carrying out the production of the U-235. Oak Ridge, Tennessee, was located in the hills of East Tennessee. There were two small towns located on the site, probably as many as 25 people in one town and 30 or 40 people in the other, so there was no great upheaval of the locality. It turned out to be a very fine locality and was selected there for the production of U-235 by the electromagnetic method. Also it was selected for the site over another valley for the gaseous diffusion method of separating U-235 isotopes and then also as the pilot plant for the determination of the proper conditions for the separation of plutonium, which as carried out on the full scale at Hanford, Washington.
At that time, the projects were very highly compartmentalized. I was given a very high classification with regard to the amount of information available to us. Incidentally, on our badges there was a Roman numeral system whereby you could immediately tell what level of detail of technical consultation you could carry out. The lowest level of course was for the work men around the plant who had nothing to do with the process, involved in the pipefitting and the manual labor. Then there was a category two for some of the operators, and a category three which was for the supervisors and then a category four, which was for more detailed information and the top category for the executive people and I was, I had available category four, which after a period of a few months was raised to category five.
So I had all of the material that was necessary to carry out all of the work at the electromagnetic plant. But there was a category higher than that which was reserved to only a few people who had access to all of the information that was going on in all of the products, in gaseous diffusion product, process, and the thermal diffusion process, and the uranium-plutonium reactor process at Hanford, but that was limited to only a few people. There were a fair number of us who managed to guess a little bit about what was going on through rumor and a few other things. But the security was quite remarkable. In spite of the fact that many people knew, afterwards, knew all of what was going on, in actual experience there were very few of us, including myself, I did not know very much about the details of the other processes. More particularly, I didn’t know what stage they had reached except that I knew, for instance, when the reactors went into operation at Hanford, I received word through more or less rumor that the temperature of the Columbia River was being raised. So you could tell immediately that the project had reached a very high powered stage. But we were worried primarily about getting the electromagnetic process underway.
My particular responsibility was concerned with the chemical process and at first I was given the title of Director of the Technical Staff for Chemical Processes. That meant that I was responsible for seeing that everything that had to do with chemistry was going all right. From the start, almost nothing was going all right. As soon as the mass spectrographs went into operation, these were tremendous magnets which were wound in a circular pattern, more or less resembling a race track and there was a matter of about a hundred of these individual mass spectrographs, enormous things, about five to six feet in radius, about 10 feet in diameter. These, each one of these had a source and a method of ionizing the uranium, accelerating the uranium until it went into an orbit and collectors were placed to collect the U-235 at the 180 degree point.
My first job was to see that the U-235 was dissolved out of the collectors and this now turned out to be enriched material which was enriched from seven tenths percent U-235 to 15 percent U-235. Since the amount of enrichment that was necessary was something like 80 to 90 percent, it was necessary to take that enriched material and put it through again. We called that first stage through alpha and we called the second stage through beta. But the first complication that we ran into was that when we performed the original experiments out at Berkeley and we had all the best chemists there that we could get. I can remember one of the very fine chemists who was actually the discoverer of carbon-14. He placed a stainless steel piece right where the U-235 was to be collected and then after a certain number of hours, the U-235 was collected on this stainless steel piece. Then we took it, and I remember showing the experiment, poured nitric acid over this stainless steel piece and the U-235 which was collected on the stainless piece dissolved magically away. So from that simple experiment it was assumed that the U-235 could be easily arranged with, be dissolved with nitric acid and then purified from that point. It turned out when we went into production, the energy of the uranium ions was greater than that of the experiment. Therefore the uranium ions actually imbedded into the stainless steel. So when we came to dissolve it out, less than 50 percent of the uranium-235 dissolved out. The rest remained buried inside the stainless steel. You can imagine the panic that ensued then.
I had seen this trouble coming from almost the first day. So, I tried to think of a way we could get around this, and thought back to my experience as an electrochemist as a graduate student. I thought well if we, since the stainless steel doesn’t dissolve in nitric acid, we can’t get the uranium practically that way. The other heroic methods would have contaminated essentially dissolved the collectors completely, and that was not practical. So I thought of the idea of coating the U-235 collector box with metallic copper and we did that by electroplating it. Then, when the uranium buried itself into the metal, it buried itself inside the copper plate, and then all you had to do was dissolve all the copper outside with nitric acid. Copper dissolves very easily with nitric acid, and left the stainless steel in the metal below untouched. Then all we had to do was recover the uranium-235 from the copper. Now, this turns out to be a little difficult because there was over 1,000 times as much copper in solution as there was uranium. No matter how good your separations are, that does pose a problem. But it turns out that the large amount of copper was actually a help because the ether extraction from a saturated solution of copper nitrate and uranium extracts at more or less quantitatively the uranium into the ether layer. The ether layer can be easily stripped of the uranium and you get pure uranium. So actually we had to devise uranium extraction method almost right as we were doing this, as we were in the process.
I can remember the first experiments were we tried this out, ether being a rather explosive and catches on fire easily. I remember carrying out the experiments and we would keep one man there with the carbon dioxide fire extinguisher and we had to evaporate some of these things, so we had a hot plate. We ran into small fires probably every half hour or so, but they were easily put out. The only thing is every time we used a fire extinguisher, there was a procedure whereby you had to write up a report, so that it was more trouble writing up the reports than it was carrying out the experiments actually. At any rate, we later found out that other solvents other than ether, are even better than ether. So we managed to solve the problem of getting the U-235 out and instead of only getting about 50 percent out, we got about 98 percent, which was, we would like to have done a little better, but was satisfactory.
So we then were piling up enough of the 15 percent uranium to make this so-called Beta process possible. When you came to the Beta process, by now the material had gotten to be very valuable, up like a factor of 100 to 1,000, so you just couldn’t afford to lose any of that valuable material. You wanted to get at least 99 percent plus. There had been a method worked out for the precipitation and recovery of the uranium because again, you had to go through the same thing. You had to work the uranium which now was very valuable, 15 percent uranium in uranium tetrachloride quantitatively. That was worked out all right. Then it had to be ionized and separated again. Now when you collected it into the proper pocket, it was 80 to 90 percent enriched uranium which was suitable for the bomb project for defense purposes. So we were now on our way to actually collecting material which could be used as a weapon. Now the problem was that the method for separating this out was not as good as it should be and again the recovery was regarded as, the low recovery was regarded as actually, potentially disastrous. It would mean that the whole process would fail unless we could do better. In the meantime, as I mentioned before, I worked out the basic chemistry of the direct peroxide precipitation and that’s where the direct process peroxide precipitation was brought into play. When it was found out that we needed this, we had to junk all of the rest of the processing equipment and in order to, since uranium peroxide does not filter well, we had to separate it with centrifuges. So we immediately got the high priority order for getting all of the centrifuges that the Sharples Company put out diverted to Oak Ridge and actually flown in on bombers so that we could install it in the so-called Beta chemistry process and we, it finally worked.
MRS. LARSON: How many centrifuges were there that you had to bring in?
MR. LARSON: The number of centrifuges we had to bring in was not all that great.
We had a number, probably about 300 centrifuges all together, because they could be used not continuously, but they could be run and then emptied and then run again. So it worked out quite well. It did require a lot of labor, but with material at that point being worth nominally, we figured $1,000 a gram, it was well worth it to put in all the labor and all the equipment that was necessary. Of course at that particular point, the volume of it was not all that great. Remember we had to produce only 100 kilograms of this in total. So that process really worked out very well.
I did have quite a controversy because people were very loathed to abandon the old processes despite the fact that it wasn’t working that well. So, I had to enlist some rather influential friends in order to make the decision go the right way. The British representative, who was a vice president for research for Imperial Chemicals of England, was there. He was a very outstanding chemist and chemical engineer. He saw immediately that the process that I recommended would be the best one to work. Then also Dr. [Charles] Krause who was former president of the American Chemical Society, very prominent chemist, he also reviewed it and said that this was the only process that would enable us to get it going. This required…
MRS. LARSON: This was the only way to get the material away from the box?
MR. LARSON: This was the only way that the recycle of that very valuable Beta material could be accomplished. This was then christened, not by me, but by the plant manager who was delighted to see this problem solved. He actually named it the Larson Process. It really was a source of delight to see that process finally work and deliver, made certain that the whole process would not come to a grinding halt because of so much material being lost or held up during the recycle. So there was a constant supply of this 15 percent material being made available to the calutron, so that what was collected in the box, the 80 to 90 percent material could then be actually turned into the bomb material which was made available then, of course, to Los Alamos for the construction of the Hiroshima bomb.
Well, this, there were a lot of other small problems along the line, but most of them worked all right. As the time went along, there were many problems over on the side of the magnets and the sources and the receivers over on the, you might say, the physics side. They had their problems, but they were worked out also at the same time. For a while it looked like the magnets would fail entirely because they kept shorting out because there was metallic impurities left by the careless welders. It looked like the whole plan would have to be shut down. But they managed to pump oil through these big coils and get all of the metallic particles which were shorting it out removed in the, by filtering them out. Incidentally, those coils which went to make up the electromagnets were wound with silver rather than copper because there was a shortage of copper during the war and also silver was a much better conductor. It turns out that there was something like about, I believe it was something like over a billion, no the figure was actually 600 million ounces of silver were used in winding the coils for the electro magnets in the Y-12 electromagnetic plant. Later on when silver got to be $10 a pound and even higher, I reflected that there were over $6 billion worth of silver in those coils.
MRS. LARSON: Could you tell us the story about how that came to Oak Ridge? How the silver was obtained?
MR. LARSON: The silver was obtained by virtue of the fact that, as I say, there was not enough copper available for these big coils and Fort Knox had all of the silver and it was just sitting there. So there was, the Army Corps of Engineers just requisitioned the silver much to the astonishment and dismay of the people at Fort Knox, but it was ordered and delivered in the proper form for winding the coils. Incidentally this was not in the form of wire because those coils were, looked more like straps, one inch wide and perhaps an eighth inch think as I remember. As a matter of fact more than that, probably a half inch thick. I remember seeing all of this silver when it was removed from these electro magnets piled up in one room, seeing hundreds of millions of dollars’ worth of silver in one room over there. Later on, I was responsible for getting that silver back to Fort Knox and that was done with some work, but not too much of a problem.
MRS. LARSON: Wasn’t it true, excuse me for interrupting, it seems to me that when the silver arrived in Oak Ridge, it was quite an occasion and all you scientists began to stay up overnight and there was a whole weekend when no one saw any man involved in that problem because you were all down winding coils, or doing something about the magnet because the silver had come.
MR. LARSON: That’s, I think that particular story is a little, a little bit mixed up because the actual winding was done outside of Oak Ridge, and then shipped in in these great big magnet boxes. But the big excitement was that when they started to be tested and they were shorted out, people worked 24 hours a day, seven days a week trying to get the shorted material out. The only time it really came to view was when we cut them apart to remove the silver. Then it was viewed for the first time in Oak Ridge. But…
MRS. LARSON: How long after was that?
MR. LARSON: That was about two years, two to three years after the war was over. But there was no silver lost as actually it probably was far more secure at Oak Ridge than it ever was before or since at Fort Knox. In theory it’s possible to rob Fort Knox, but it was never possible to take one of those great big magnetic cases and cut them apart outside of an invasion by an Army. But at any rate there were a lot of problems to be unraveled and perhaps you could go on for…
MRS. LARSON: Well, I would like to interrupt one more time on that magnet story which I think is so dramatic and ask you did the treasury deliver the silver to you in the form of those straps that were…
MR. LARSON: No, the silver was delivered actually to the manufacturer of the great big electromagnetic boxes and…
MRS. LARSON: Who was that? Is it possible to say?
MR. LARSON: This was Alice Chambers in the case of the Alphas and Westinghouse in the case of the Betas. Those…
MRS. LARSON: They fashioned the…
MR. LARSON: They fashioned it. They had to take the ingots and fashion them into the proper size and so on.
MRS. LARSON: Straps which were then wound.
MR. LARSON: Straps which were then wound in the proper way to make the electromagnets. As I say it wasn’t rather dramatic that there was that much silver tied up for that purpose, but…
MRS. LARSON: It was the entire treasury of the United States.
MR. LARSON: It was literally probably 98 percent of all of the available silver in the United States, put in there for that particular purpose, but since it was just being stored, it performed a useful purpose, other than just sitting there during the war.
MRS. LARSON: You’re so modest. Do you think that today something like that could be accomplished even.
MR. LARSON: Well, certainly not in peace time. In order to get something like that done, the, probably it might take essentially years to unravel the red tape for such a transaction. Where as in those days, of course, there was, and rightly so, there was nothing that was needed for the war effort that was left undone. Fortunately the Manhattan Project had the top priority of all of the projects, much to the disgust of the Naval and Army and Air Force projects which were under way.
MRS. LARSON: Well couldn’t it also be said to the credit of the Manhattan Project, all that silver to the last half ounce was returned.
MR. LARSON: Well of course, later on I became superintendent of the Y-12 plant in 1948 and at that time we had the task of returning all of that silver and for all practical purposes, as close as you could weigh it, it was 100 percent. At least it was 99.99.
[Break in video]
MR. LARSON: Toward the end of June and the beginning of July, it was very apparent that we had a big effort being mounted in order to scrape together all of the U-235 that was available. There was no stone unturned to get every milligram of U-235 delivered to Los Alamos. It was about July 25 that General Groves came to Y-12 and we had about 20 to 25 of the key people involved meet together for lunch. General Groves was usually a very hard looking, hard driving individual with very little apparent sense of humor and no trace of humor in his eyes. However at this particular luncheon I have never seen a man in as good a spirits as General Groves. In fact looking at it in retrospect, I would say that his facial expressions on that day probably constituted a grave breach of security. It was obvious that he knew something that we did not know at the time. He, in his speech, indicated that we are now certain of the success of the project that we have now, which we had worked on for such a long time, never a hint of what caused great optimism on his part. Of course in retrospect we knew that it was a little over a week before they had exploded a bomb at Alamogordo and it was a complete success, where as he showed in his speech, no hint whatsoever of this particular event. All of us were puzzled at the enthusiasm which he showed. Of course, it was only about ten days later, it became abundantly clear to all of us why he was so happy that day. Well on August 5, we, of course, were working at our usual tasks in order to advance each one of the processes, refining everything, making sure that everything worked properly, ironing out bugs of course which continued to arise, and suddenly into my office, someone burst in and said, “They dropped the bomb.” I looked up and, of course, we had waited for this for a long time. My immediate instinctive reaction was to reply, “Did it go off?” Always in the back of our minds was the fact that there probably was no difficulty once you had U-235 in the proper quantities that you could make the chain reaction operate. What was concerning most of it, most of us, was the simple fact would it go off and fizzle so that there would really be no effect. Well the answer became abundantly clear in the announcements of President Truman which came on all of the radios, that the bomb was dropped on Hiroshima with the force of 20,000 tons of TNT and that, as a military weapon, the bomb was completely successful. Of course, about a week later, after leaflets were dropped and there was no positive indication that the Japanese were about to surrender, a second bomb was dropped on Nagasaki and, of course, practically immediately afterwards the Japanese surrender negotiations took place and hostilities ceased. This was a moment of great relief to all of us and we felt that our mission had been accomplished.
Well, after this had been accomplished, we began to review the things that we were doing and what meaning they had in light of the changed circumstances. It became very evident within a few months that the gaseous diffusion plant which had very limited production up to the last few weeks of the end of the war now began to produce material with great efficiency and great quantity and the so-called alpha units were immediately obsolete as compared to what could be done with the gaseous diffusion plant. Consequently within a few months, the alpha units were shut down and left the electromagnetic plant only with the task of taking the 12 to 14 enriched material from the gaseous diffusion plant and bringing it in the beta units up to the required bomb strength, or 80 to 90 percent. Of course after this, within a year the gaseous diffusion plant showed the ability to take the material all the way up to bomb strength material. It was then decided to shut down the plant, the beta units, and take over only that part of the operations which had to do with the conversion to the tetrachloride and a few miscellaneous things, and continue work on the research and development on the electromagnetic process in case certain improvements which would make it economical to continue.
Well, as far as the chemistry was concerned, which was my main responsibility, I decided that we should take a look at our whole operation and see what other purposes could be served by the skilled chemists that we had assembled there. As a result of several conferences which we had, we decided that there were three areas which could be actually worked on with great potential profit to the whole nuclear energy effort. One of them was the task of separating isotopes by chemical means. So we turned our attention to separating lithium-6 from lithium-7 because lithium-7 had a very low cross section and could therefore be used as a reactor coolant in the program which might eventually develop to use a reactor for electric power generating purposes.
Another possibility of great interest was the great skill which had been developed in the chemical research group in separation of materials which had really not been available previously. Since the group had acquired a great skill in solvent extraction the question was asked, “Are there better methods for the separation of uranium from the ores?” It became very evident that as the possibilities for the peaceful uses of atomic energy would develop, we would need tremendous quantities of uranium and those quantities would have to be from continually decreasing enrichment. In other words, when the first materials were, had come from the Belgian Congo or even from Canada, it was sometimes possible to get 10 and 20 percent ore and it became evident as we went to the United States sources, the content of uranium would be below one percent. So it was decided to investigate better methods for getting uranium out of these ores.
It soon became evident that there was a third very important problem so far as chemical separations were concerned and that is the need for highly purified zirconium. It turns out that in nature, zirconium is always contaminated with sister element, hafnium which is right below it in the periodic table. Hafnium is extremely difficult to separate from zirconium. In fact it had only been done on an experimental scale with great effort of fractional crystallization and literally hundreds of stages were necessary to purify the zirconium away from the hafnium. Now why is it necessary to separate the zirconium from hafnium? In order to use zirconium in a nuclear reactor, it must have the properties of having a very low cross section and not poison the reactor because of its absorption of neutrons and it turns out that all of the zirconium which was available had contamination by hafnium and was unsuitable. There is no more difficult separation in the whole periodic table than the separation of zirconium from hafnium and therefore it was an extremely expensive operation. In order to do this by fractional crystallization, the cost would be over $100 a pound.
Well, it was decided to use the modern techniques of solvent extraction which would be very much more selective in its ability to perform this separation. It was found that a thiocyanate complex of zirconium and hafnium made it possible to separate zirconium from hafnium by counter current extraction to a purity never before obtained and at a cost which was only one-one hundredth of the cost of fractional crystallization. This made possible the availability of zirconium for reactors and it was, the first use was made in the actual first submarine reactor, the Nautilus. I have here in my hand a small example of hafnium-free zirconium metal which was produced for the batches that went into the Nautilus fuel-element cladding and made possible the fine fuel elements that the Nautilus had. This was all done by the extraction method and all of it done in our research and development laboratories which produced all of the zirconium for the first nuclear submarine. So there was one triumph of new techniques of solvent extraction for the separation of very difficult materials.
The next important problem turned out to be a rather unusual one in that there never did develop a need for pure lithium-7, but for the weapons program, the, it became necessary to develop a method whereby lithium-6 could be delivered free from lithium-7 for purposes, for defense purposes. This was again thought to be very expensive, but it was found that a method whereby the counter current extraction again in a very special way, could be used. Actually using some of the techniques that we used during the war, it was possible to produce very adequate quantities of lithium-6 for defense purposes and there was a need for experimental reactors. A certain amount of lithium-7 was also produced by this particular method.
With regard to obtaining cheaper methods for getting uranium out of ores, again solvent extraction was very successful. At least at one time, almost 75 percent of the uranium which was produced in the world, used the solvent extraction method which was developed by this chemistry group in the electromagnetic plant. So starting from a conference held immediately after the war to determine the skills which this group could apply themselves to, three tremendously important projects were completed which had great economic significance to the old nuclear energy effort and great importance to the defense effort.
So this particular, at this particular time after the completion of some of these projects, I was asked to become director of the Oak Ridge National Laboratory, and in 1950, I assumed the responsibilities as director of the Oak Ridge National Laboratory. There, of course, I encountered a fantastic number of new problems. Dr. [Alvin] Weinberg, who was a research director, had organized a very fine program. Dr. [Eugene] Wigner who preceded him also started a number of very important programs. The Oak Ridge National Laboratory had the responsibility to help develop the so-called materials testing reactor which was a reactor which was designed to furnish a high flux of neutrons and consisted of fuel elements of aluminum and uranium, which in the proper configuration with water flowing through and so on, developed a very fine reactor for test purposes. The reactor was actually constructed in Idaho, much of the actual parts were done right at the Oak Ridge National Laboratory in our shops, and I made several trips to Idaho to help work with the Argonne National Laboratory group in actually finishing that reactor.
At the same time, there became evident the need for better methods for separating the fission products and plutonium and uranium. The original process as designed for the use at Hanford separated out the plutonium, but left the uranium and fission products together and they were both stored in big tanks out at the Hanford plant. Of course as the operations proceeded and plutonium was extracted from these, great quantities of uranium piled up in these tanks and there was a great economic incentive to develop a process which would separate out the plutonium and then also separate out the uranium and leaving the fission products by themselves. Well at that particular time, there was a compound discovered, trybutyl phosphate which with proper extraction agents would do a wonderful job of fitting into and separating out uranium away from plutonium and plutonium away from the fission products. So we had solved this particular problem and it was called the PUREX [plutonium-uranium redox extraction] process for plutonium-uranium extraction. This was actually put in at the Hanford plant for some of the processing. All of the processing at the Savannah River Plant which was constructed during this period used the PUREX plan and to this day throughout the world, the PUREX process slightly modified is still being used for the processing of spent fuel.
In addition to this, of course, the Oak Ridge National Laboratory participated in the project design to furnish a reactor which would be suitable for airplane propulsion. At that time, there was a concept which was developed using a molten salt which contained U-235 which circulated as a fluid fuel reactor. On the experimental scale it worked very well and in addition to that it showed great promise in a continually operating plant whereby the fuel reprocessing could be done more or less continuously. Unfortunately the project did not get very much attention from the industrial companies, but it was a great success as an experimental reactor which would accomplish that objective, if that objective ever appears to have validity in the future.
Another project of great interest at that time was the gas cooled reactor. There was very much pioneering work being done on the gas cooled reactor and subsequent reactors, which were built in Colorado and another one in Germany. It used much of the technology developed at the Oak Ridge National Laboratory at that time.
Perhaps one of the most interesting things that developed during that time was the participation of the Oak Ridge National Laboratory in the Atoms for Peace Conference. It was on December 8, 1953, that President Eisenhower delivered a speech at the United Nations offering to contribute both enriched uranium and scientific and technical knowhow for peaceful purposes. This caught the imagination of the world and subsequently a conference was arranged to be held in Geneva in July and August of 1955 and the entire world sent representatives to that conference. In addition to many of the exhibits involving radioisotopes, there was a very interesting exhibit which I think really made the success, exhibit-wise, of the whole conference. About six months before the conference was due to open, Dr. Tom Cole and Al Weinberg came to the office to discuss offering to actually construct a reactor and place it in position in Geneva to actually have an operating reactor right on site for the Atoms for Peace Conference. It sounded very daring and almost foolhardy at the time, and today of course it would be unthinkable. But in the short period of six months an operating reactor was constructed and all of the parts were put together in Oak Ridge and tested and placed on a plane for Geneva where we had a crew waiting to put the reactor together in a building which was designed and put up for the occasion just to emphasize the peaceful nature of the exhibit. It was placed in a building which had somewhat of a resemblance to a Swiss chalet. It was very efficiently designed building and served the purpose for housing the reactor and the accompanying exhibits very well and indeed was the hit of the conference. I can very well remember that Lewis Strauss who was then the Commissioner of the Atomic Energy Commission said that he had seen an awful lot of exhibits and a lot of exhibitions that were very wonderful, but were completed the week after the exhibit closed. He wanted nothing to do with such an exhibit. Consequently, we scheduled the construction and operation of that reactor practically down so that every hour was accounted for and nobody was allowed to fall behind in the design and construction of this reactor.
Well, there were literally dozens of other very outstanding programs that were carried out during the period of 1950 to ’55 and it probably was one of the most exciting periods of my life to actually go through and see the successful completion, some of which I observed in the test tube and then brought to fruition in multi-hundred million dollar projects that operated very successfully from the start.
[End of Interview]
PIONEERS IN SCIENCE AND TECHNOLOGY SERIES
ORAL HISTORY OF CLARENCE LARSON
Date Unknown
Transcribed by Jordan Reed
MR. LARSON: This is a test of lighting and exposure and it will be very interesting to see how this looks on the playback. First I am going to put on my coat and try that. All right and this will be the format of the recording which I plan to make now. What I am going to do is first start out with my primary interests at the end of graduate school in things that had to do with radioactivity following it up with my experiences at the College of the Pacific, now the University of the Pacific and with subsequent experience in being recruited for the radiation laboratory at the University of California which then lead to Oak Ridge and the exciting days there.
[Break in video]
MRS. LARSON: Okay, anything else you can think of I can buy…
MR. LARSON: Nothing more.
MRS. LARSON: Okay.
MR. LARSON: Fine. I am recording now.
MRS. LARSON: Oh, sorry.
MR. LARSON: So your voice is on there for posterity now. So this is a test to see if the audio is sufficient. I moved the camera back fairly far because this will give me more depth of focus on the subject and I think it will be much better if we can put the camera back further and then light accordingly. This will give us a more depth of focus on the subject and I think in general a much more pleasing appearance. The main thing of it is when we go back this far, is the audio still functioning. All right. We will try the test now.
[Break in video]
MR. LARSON: This next test is to determine whether or not I get better light distribution with a reflector over on the right hand side. I think just by visual inspection I don’t think that it makes all that much difference, but I think the only way we will be able to determine that is to watch carefully and analyze the playback to see whether it functions properly. I think we’ve got enough here now so that we can see if we made any improvement what-so-ever.
[Break in video]
[Dog barking]
MR. LARSON: Quiet, please.
[Dog barking]
MR. LARSON: This is the first test draft of the actual interview. My… cut. Cut.
[Dog barking]
MR. LARSON: All right. After that brief interruption caused by my good friend Prince, I will start this interview from scratch. Let’s take one. My story begins with some experiences I had in graduate school, which ultimately lead me into the Manhattan Project. We, as a graduate student, I did not work in radioactivity, but I did some research work on the role of electrochemical phenomena and physical-chemical phenomena and the relationship between inorganic compounds and organic compounds. So as a consequence, I did manage to get a fair understanding of the field of inorganic chemistry which was to play a very key role in my subsequent interests. My acquaintance with radioactivity and nuclear physics, of course, grew out of the fact that I was present at Berkeley, at graduate school during the exciting years when E.O. Lawrence was developing the cyclotron. I can remember distinctly attending one of our graduate science meetings when there was radioactive sodium produced in the cyclotron and a demonstration was made of the speed of absorption of sodium ions into the blood stream. In order to carry this out, a preparation was made containing radioactive sodium chloride and the subject drank this. Of course, it was a very low level, so there was absolutely no danger and then the Geiger counter was placed at the fingertips. It was really amazing. I think it was something like 35 seconds after drinking this that radioactivity began to appear in my, in the fingertips of the subject. So that was quiet a spectacular demonstration of the early uses of radio isotopes in the field of medicine. Of course, after the discovery of the neutron and after the discovery that artificial radioactive isotopes could be made by either bombarding neutrons, or by deuterons or by other suitable atomic projectiles, this was a very important and very active field of science immediately after 1935.
I can, very early memory remember the discussion of the discovery of artificial radioactivity and the sensation that it made during the years approximately, about, beginning in about 1935. Well, to make a long story short, almost immediately thereafter I took a position as professor of chemistry at the University of the Pacific, then called the College of the Pacific, where I spent five wonderful years as a teacher of inorganic and physical chemistry. During those years I maintained my interest in the spectacular field of radioactivity and I made arrangements with E.O. Lawrence to obtain some of the target material that was used to hold the particular element being irradiated. In other words, whenever someone wanted to carry out an experiment they put it in a holder and then the particular element was then bombarded with deuterons and then subsequently taken off the target to be worked up and the experiments carried out and the indemnification of the radioactivity made. Then, of course, there is sufficient stray deuterons that would hit the holder of the target and I was able to get some of the old targets which had of course iron, chromium and, I believe, some of the other, cobalt, and some of the other materials used to make stainless steel. So consequently, there was a slight amount of radioactivity which was generated as a result of the stray deuterons hitting these targets. Of course, the radioactivity was very small but adequate for experimental purposes. I think took these targets and dissolved them then using chemical separation methods. I was able to separate out several radioactive elements. At the time, of course, there was nothing new about these radio elements so I was not in a position to discover any new radioactive elements, but I was able to use the fact that we did have radioactivity to use in actual experiments to determine more efficient separation methods. In order to separate out, say iron, or cobalt, or manganese, or chromium from this mixture it was necessary to subject it to chemical methods, precipitate the different elements with different reagents and then actually get other methods developed, such as extraction and so forth, so that by doing this, I was able to sharpen my skills in the separation of one element from another, which was to play a real dominant part in my subsequent work on the Manhattan Project.
In order to do this of course you had to have a method for detecting radioactivity. As strange as it may seem, in those days, the Geiger counter had been invented long before that, but they were quite expensive and quite erratic and quite difficult to operate. However, Dr. Lauritsen of Cal Tech had invented a quartz fiber electroscope in which he used gold plated quartz fibers with those, electric charges placed on that. Of course the fibers would fly apart and then a scale was put in the back and this was put inside of an optical device so that you read it by looking in the view piece. Then by actually timing the decay of the radioisotope I was able to determine the relative activities. This was a very useful tool. In fact, I have talked to Glenn Seaborg quite recently and he mentioned to me, whereas most of the time he used the Geiger counter, he did find the Lauritsen electroscope a very useful tool, in fact almost superior to the Geiger counter at that time for certain purposes. This introduced me to radioisotopes and the actual ways in which you could use separation methods and it was a very fascinating field. In fact, one of the things that I did at that time was to develop a method for determining the amount of sulfate in very dilute solutions and by using radioactive chromium as a tracer, I was able to develop a rather crude method. About 15 years later, I went back in the laboratory, back in Oak Ridge, with modern techniques, modern apparatus, and I was able to develop this and actually wrote a short paper on the use of radioactive methods for the determination of sulfate. A rather non-significant contribution, but a very interesting one. The subsequent to that, of course, I was in coincident with that, I was very busy with my work as a professor and this kept me very well occupied. In fact, at that time, with really tight budgets, compared to budgets in colleges these days, we were expected to teach the equivalent of 15 lectures a week, of course, with the additional responsibility of running the examinations and tests and preparatory and laboratory work, so it did not leave me too much time for research work.
However, one of the things that I can remember in our teaching experience was that we would have a seminar every Monday afternoon to discuss recent findings in the field of chemistry and for this particular Monday afternoon I had read about the discovery of the Hahn and Strassman and the demonstration of the fissioning of the uranium atom. This was a very significant device. Here, in this one article, which did not occupy too significant a space in the journal, immediately all of those of us who could, were familiar with the field, and, this was worldwide, we could see immediately this was the key to unlocking the energy of the atom. Something that people knew could ultimately be done, but there was absolutely no progress in doing it in such a way that could be practical. All other attempts to unlock energy from the atom resulted in more energy being put into it than was, than you could get out of it. In this particular case, there were perhaps 100,000 or even an infinite amount of energy gained in the process of fission. So we spent that particular period actually discussing the implications of that new development in science.
At that particular time of course, the word fission was not used. I have a story somewhat later as to how the term fission originated. But this was very interesting and then, of course, within the next six months, articles appeared in the popular press as to the implications of this and speculation. But sure enough so far as scientific mention of this is concerned, this immediately dried up. No articles appeared in any of the journals and at first there was a self-imposed secrecy on the part of the scientists and, of course, later there was a government imposed secrecy there.
Well, as a result of the bombing of Pearl Harbor in December 1941, of course the nation geared up for war. Into our college, of course, we brought in courses of teaching fundamentals for development of aviators and the time was quite confusing. At the end of that term, I received a call from Berkeley to come down there to be interviewed for an important project. I must confess that until I actually appeared for the interview, I had no idea of what the project was. As a matter of fact, during the interview, the only reference was to a project of national importance and actually the word was used that the successful completion of this project would result in ending the war. So with that little information I decided to take a leave of absence from the College of the Pacific and arrived in Berkeley in June of 1942. There, of course, I soon learned what the project was all about. My first task in joining the project was to help out in preparing chemical compounds of uranium for use in the project. At that time, of course, we did not use the word uranium. The code word tubealloy was used instead. So that we never discussed any of the compounds or any of the results in any terms other than compounds of tubealloy and percentage composition of tubealloy and so forth and so on. For example if you wanted to refer to uranium dioxide, it was always tubealloy dioxide.
So another interesting thing was that the books containing the chemistry of uranium were actually removed from the shelves of the library. They were sequestered inside for the use of the project at the radiation laboratory at the University. One of my first jobs was probably pretty illegal, was to copy the reference book on the chemistry of uranium and I did this at home by using photographic methods. It proved, actually there was never a day that would go by where I didn’t refer to this reference work. It was absolutely essential to have all of the knowledge of the chemistry of uranium as we progressed.
Well this, my first job as I mentioned was to take uranium tetrachloride in an impure form and distill it. Now uranium tetrachloride is a solid material and it distills only at high temperature and perfect vacuum must be used. So we had heaters at the bottom of our vessel and then a cold, cooled spot at the top and then we would actually pump that down to, not a perfect vacuum, but a good vacuum, and start the distillation. Well this sounds a little easy, but this was my first experience in vacuum leak testing. That is a whole history in itself, but anyone who has done work in an evacuating apparatus knows that there are an infinite number of leaks that can take place and finding where those are really got to be quite a task. As a matter of fact, I was able to determine when I had plugged up the leak sometimes, but just listening to the vacuum pump and the change in the clicking of the vacuum pump determined whether or not you were making any progress. Of course, we had very refined gauges to determine the ultimate vacuum. I believe those were called McCloud gauges at that time. Since that time, of course, the art of leak detection has really advanced so that people have a very easy time of it these days.
Well, I was able to produce this uranium tetrachloride in a pure form and then we were, had to do this all in absolutely dry atmosphere because uranium tetrachloride is very hydroscopic. So we would do this inside a so-called glove box which is simply a box which is three feet by three feet by three feet with a glass front which holes cut into it and rubber gloves, sealed. You would place your material in there and then carry out whatever operations, either taking it out of the vessel where it had been distilled, or loading it into a vessel which is needed for subsequent operation.
The subsequent operation, of course, turned out to be that uranium tetrachloride was the material to use as a source material for the so-called calutron which was essentially a very large mass spectrometer. Now the mass spectrometer for those of you who don’t know it is a method by which you can separate isotopes into its component parts. Since uranium had two main isotopes, U-235 and U-238, you would place this uranium tetrachloride inside a vessel which in turn was in a magnetic field. Then the vapor from this was actually ionized and the uranium ions were sucked out by means of an accelerating electrode and they would go out into this space and be turned by the magnetic field. By the time it reached the 180 degree point, it was separated into two components, the U-235 component and the U-238 component. When I joined the project the most they had ever been able to separate up to that time was about one milligram of partially enriched U-235 and E.O. Lawrence told me that our objective was to make 80 kilograms of this material by July of 1945. Now this is three years, and up to that time, and this had to be relatively pure, up to that time we had one milligram of that. Well as you see, we had to make almost a billion times that amount in order to accomplish our objective.
So we set out and solved the problems of making the uranium tetrachloride and making it pure. I investigated then other methods for making the uranium tetrachloride. One method we had was to make uranium pentafluoride, which could be done by cooking uranium oxide in uranium, in carbon tetrachloride under pressure and heat and the conversion then resulted in uranium pertafluoride. Then, you had to take the uranium pentafluoride and actually separate it into uranium tetrachloride and uranium and some other compound. At first, it was thought all we did when we heated this was to drive off chlorine and so instead of having five chlorines you would end up with four. However, I found that if I were to do this carefully and distill it, there was a brown substance that was collected on part of the tube. This brown substance turned out to be uranium hexachloride. Now, people have postulated that uranium hexafluoride could exist, but the size of the chlorine molecule would make it impossible to make it fit six around the uranium molecule. I had quite a number of skeptics on this, but I finally proved the point and actually wrote up this as one of the discoveries of our group. I was very proud to have persisted in proving that this could exist. Soon after that we heard and this was kept very hush-hush except for very few people, that the project was promising enough and we went from a milligram, to 100 milligrams, to a gram and so forth. After about a year we were in the, almost in the kilogram state of the slightly enriched uranium. So we were confident at that point that we could scale up the process. Consequently the decision was made to go to a site in Tennessee which subsequently was called Oak Ridge in order to carry out the big industrial scale that was necessary to produce the quantities necessary for our war effort.
Well, one of the things that became obvious was that we needed two stages in order to carry this out. The first stage was to, would bring the uranium up to an enrichment of about 12 percent and 88 percent U-235 starting with less than one percent. Then you had to take that material and put it through again which would bring it up to 80 or 90 percent which was necessary to make a nuclear weapon. So we had, these two stages were called Alpha and Beta. As you can readily see, by the time the material got to be fed into the Beta stage, the material had got to be very, very expensive. So the, we looked at various and sundry problems along the way.
My first problem that vexed us was the fact that when the uranium traveled in these large vacuum chambers and was collected in a collector, in a stainless steel collector, it was found that the material had high enough energy that it buried itself into the stainless steel collector and it was impossible to dissolve it out by ordinary means. Now in our original experiments in Berkeley, we had put a stainless steel collector in a beam and collected some uranium. Then you took that stainless steel piece and used concentrated nitric and it dissolved off beautifully, however that was at considerably lower speeds. So when you got to the high energies in the production plant, that uranium just embedded itself inside the stainless steel and consequently only 30 to 50 percent of the material appeared as product.
This alarmed people very much, naturally and I, as soon as I saw this particular problem, I was fortunate enough to have on my staff a man who had considerable experience in electroplating in industry. I got the idea, the thing to do is to actually electroplate the uranium with the copper. Then copper, the uranium would go inside the copper, but copper dissolves very easily in nitric acid, so you could bring the uranium into solution without any trouble. So we worked out the method of doing this. We set up electroplating baths, actually using the industrial sinks which looked very much like laundry tubs, but we were able to do this in a very rapid form.
As a matter of fact, I can remember a conversation with E.O. Lawrence and I told him of my findings on this and he asked, I asked him, well, should we go ahead and of course he said, go ahead immediately. I said well, we’ll probably be able to put this into operation in about two weeks. He said, “I want every receiver that goes into these units electroplated by tomorrow morning.” We worked 24 hours around the clock. Sure enough, we were able to set up some lines so that we could feed some of these receivers in. We didn’t quite make the 48 hour deadline, the 24 hour deadline, but we were able to do this in about 48 hours. We completely changed the process in that short a time. Well, this gave rise to some other problems. However, at this time I think I’ll just stop here and see how this sounds so far.
[Break in video]
MR. LARSON: This is another test with additional lights. As a matter of fact I have added 150 watt flood light immediately above the subject so that I think we will get very much better and more even lighting with this. But there is no other way to find out but to test it. So I hope that this will, this additional lighting will show up in the proper way. If it works out we’ll have a much better set up as far as attempting to actually make documentaries of people in a more relaxed fashion. I think that also with this particular lighting, I think that it is much less obtrusive to the eye, but let’s see what it looks like. We may not like it at all. So at this time we’ll cut and rerun.
[End of Interview]

Click tabs to swap between content that is broken into logical sections.

PIONEERS IN SCIENCE AND TECHNOLOGY SERIES
ORAL HISTORY OF CLARENCE LARSON
Interviewed and Filmed by Jane Larson
Date Unknown
Transcribed by Jordan Reed
MR. LARSON: My name is Clarence Larson and I am director of the Pioneers of Science and Technology video tape project. The first part of this is an experiment which I am going to give some of my biographical information starting essentially from the time I was born in 1909 in the town of Cloquet, Minnesota, which is in the northern part of the state near Lake Superior.
My earliest recollection of any happenings and many psychologists and students of child psychology will dispute this is a vague recollection of my mother taking me in her arms outside and pointing to something which was a light. And vaguely in later years I tended to associate that with the appearance of Halley’s Comet in 1910. Theoretically, this was too young for any such memory to exist, but I just recite this as an interesting background because now, next year, we are faced with the return of Halley’s Comet. My early childhood was really quite uneventful. Our town was a homogeneous town primarily devoted to lumber manufacture and paper manufacture and slightly later it was devoted somewhat to the manufacture of insulation. In fact I believe the first manufactured insulation was made of fiber wood which was placed between two sandwiches which gave an insulating property for the insulation of houses.
My first recollection of a big event in my life was the so-called Big Fire of 1918. The fall of 1918 which incidentally was the last of World War I, was a very, very dry summer and the woods were tender dry. Of course that brings on the possibility of very serious forest fires because at that time Minnesota was a lush grove of timber. Surely enough, a large forest fire broke out and within a day, our town was endangered. When we saw the fire coming and we had also heard reports from the train crews coming through, of the serious fires down below us, where by a town of about 500 was completely wiped out with grave loss of life. As the fire approached our town, all of us were able to escape due to the foresight of a train dispatcher, who held all of the trains coming through including boxcars, coal cars, passenger trains, any form of transportation that was available was held so that we could evacuate the entire town of 10,000 within a few hours. I doubt even with our modern planning and everything that you could have arranged such an efficient evacuation with no loss of life during that short period of time. At the time, I was nine years old, and of course, to this day, I have a vivid recollection of the tremendous wind storm which was the characteristic of the fire storm, the wind being actually generated by the tremendous fires that were, that broke out.
[Break in video]
MR. LARSON: As you can readily see, this was a very traumatic time with the entire town being evacuated and sent to Duluth and Superior over the rails. At that time there were practically no automobiles in existence in our home town. Perhaps maybe five or six automobiles were in existence. Roads were very poor, one and a half lane roads between Cloquet and Duluth. Unfortunately, those people who did try to get away by car were burned to death because they were caught on the road by the fires. So fortunately, practically the whole town was saved by being evacuated to Duluth and Superior. Temporarily, we were brought to centers, school gymnasiums, civic centers and places like that. The people of Duluth and Superior were mobilized and took them, took each one of the, families who volunteered, took one family from Cloquet and so we were temporarily quartered in people’s homes in Duluth and Superior, an outpouring of real generosity on the part of the people. I will never forget the cordial reception we had from the people of Superior, Wisconsin. Well, following that, to make a long story short, we did rebuild the city of Cloquet. At first we lived in temporary housing and then build a permanent house, which stands to this day and which I have visited just last year.
Following that, it was about time for me to go to high school and there was nothing particularly outstanding in high school. Before I went to high school, I had the opportunity to participate in an educational experiment. We hear of all kinds of educational experiments today, and this was no exception. They gave all of us a test in the sixth grade, and if we scored high enough, there were I think 25 of us selected to go into a special class which would study both seventh and eighth grade subjects together. This included math and, of course, it was advanced arithmetic, and algebra, literature, writing and some history and most notably, great emphasis was put on spelling. At the end of that time, it was time to give us examinations, and these examinations were not trivial. The examinations, from the seventh grade on through the finish of high school at that time, were conducted by the state education department so that in order for us to go into high school, we were forced to take state generated tests in both seventh and eighth grade subjects and pass both of them in order to receive credit. As a result of this experiment, four of us passed into high school and the rest of them had some deficiencies which they had to make up before they could be full term freshman. But four of us made it into the regular high school classes and therefore I was one year ahead. As a result when I went to, went into my senior year, I was 15 starting my senior year. So I graduated quite early.
During, particularly my freshman and sophomore year and perhaps even in the eighth grade, I became very interested in electricity and I read every book in the library on the subject and decided to perform some experiments. So we rigged up a little telegraph line between my home and some of my friends and neighbors and we were able to communicate back and forth through these lines. We made the telegraph ourselves, [inaudible] coils. In order to get the battery power, we scrounged around the Bell telephone discard pile and they used to use batteries in the phones in those days. The used batteries had enough electricity, electric power, energy left in them so that we could use them in this purpose by connecting them in series and parallel. So we had a great deal of fun with this and then shortly after I became interested in wireless, and at that particular time, in 1920 and ’21, it was actually before the days of broadcasting. I believe broadcasting started around 1921 and as a generator of radio frequency signals we used the, a spark gap. My source of a spark gap was a Ford spark coil which I connected to the batteries and generated about a half inch spark, connected that to an antenna and we were able to actually signal as far away as about one and a half miles using this set up. So I became interested in electronics and electricity at a very early age.
During my high school years, strangely enough I had not really intended to go away to college. Remember this was back in 1924, 1925 and ’26, and in our hometown a very small percentage of the graduates went on to college. I did not expect actually to do so. In spite of the fact that I got reasonably good grades, I was not at that top of my class or anything. So I decided after I graduated that I would attempt to get some sort of a job and then work up from there. Most people, my brothers had both obtained jobs at the lumber and paper companies there in town and I thought I would follow along the same path.
However, I was given the opportunity to do boys work at the local YMCA and strangely enough I was offered for those days, quite a handsome salary in order to do this. So as a 16-year-old, I became a full time employee as assistant YMCA secretary for boys work. I got this particular job because I was actually very interested in the Bible at that time. In fact, I read considerably and I was active in the youth groups in the church and so on. Although I never thought about it particularly, I suppose that was why I happened to get this job. Well as a result of this, I was given the opportunity to participate in organizing boys’ tournaments in basketball and soccer and tennis, all kinds of activities of this type. Also occasionally since the YMCA was religion-oriented I was called upon occasionally to serve as a substitute minister in some of the small churches in the rural communities. So, I would occasionally go out and give the service and the sermon of that time. As a matter of fact, I think I still could today give the sermon which I gave at that time, which was my favorite one with the title of, taken from the Bible, and Jacob’s Well Was There, has the theme, of course, that the fact that Jacob had done some very fine work in drilling that well, digging that well. People for generations afterwards benefitted from the work that he did during his lifetime. So I think there was a very fine moral lesson to that and it was, as I say, I can still remember that particular sermon that I gave.
Well, as time went on and I read more and more I became more interested in the possibility of going to college and of course actually probably as soon as I started the job I began to think, perhaps if I saved my money I would be able to actually go away and get an education in college. So I saved a reasonable amount of money and with some trepidation, decided to quit my job, which incidentally by that time was paying for those days an enormous salary. I believe it was $125 a month, which was a very good salary and enrolled at the university and took the usual courses. I had become interested in chemistry. So I thought that I would end up as a chemistry teacher after I graduated from college, but as I grew more and more interested as I went through college, I decided that if I could I would go on to graduate work, or perhaps work in industry. I grew less and less interested in education courses. As a matter of fact I became very bored with the education courses and did not like them at all compared to the scientific, mathematical, and technical courses that I took. So, as a, to make a long story short again, I graduated in the depth of the Depression. This was 1932 and not a member of my graduating class in chemistry received a job offer, with the exception of one man who got on offer from his uncle who owned a small chemical plant.
So, I was fortunate in getting a fellowship at the University of California and decided to move to California. My mother was quite tearful about this, moving so far away, but I really enjoyed the challenge and looked forward to it and journeyed to California where I did my graduate work. This was in 1932 and as I lived through those graduate years, I did not realize what a revolution in science was beginning to occur right around me. The, it was at that time, actually in 1932 that E.L. Lawrence invented the cyclotron and of course I naturally was conscious of it, but I did not have the full realization of the revolution that that made in physics. My work of course was in chemistry and my, some of my work that I did, involved the physical chemical properties of biologically important compounds. As a result, I studied the electrochemistry of these compounds; its behavior in electric fields determined the electrode potentials of various systems and had learned a great deal in addition to chemistry, learned a great deal about electrochemistry which was to serve me in good stead later on. Well to again, make a long story short, I was, I finally received my Ph.D. and by that time, of course, there were two avenues open to me. One I could go into research work and the other I would go into teaching.
As a matter of fact, I received a full time research assistantship at the Mount Zion Research Foundation almost coincident with finishing up my thesis work for my Ph.D. degree. So I did research work for a year and learned about an opportunity for an instructorship at the College of the Pacific at that time. I was very pleased to do this because I actually felt college teaching would be an ideal life. You could do some research work and also, I always did enjoy teaching, particularly at the elementary college level. So I did obtain the position. I found out later that there were actually 100 applicants for this position. I didn’t realize at the time how lucky I was to actually obtain the position. I found out later when I became head of the department that those applications were on file. So I glanced through them and I must say that I never could quite figure out why they hired me rather than some of the very well qualified people that they had. At any rate I was very happy to obtain the position and my years of teaching there at the college were very happy years. I think that the combination of a small liberal arts college together with small classes forms an ideal situation. In addition to that, I did have a little opportunity to do some research work and since my work in graduate school brought me into touch with the marvelous developments going on in the field of, the development of artificial radioactivity, the application of the cyclotron to radioactivity.
I did not actually participate in that because I was so busy trying to iron out my own research, but I can remember distinctly one, attending a lecture given by Dr. John Lawrence, the brother of E.L. Lawrence in which he demonstrated the radio, the absorption of radioactive tracers. They had produced some radioactive sodium in the cyclotron, dissolved it in water and mixed it with perhaps some lemonade or something. They had as a demonstration, they had one of the workers there drink the radioactive sodium which is in the form of radioactive chloride. They had a Geiger counter on the finger which was extended away from the Geiger counter and perhaps, within about two or three minutes, the Geiger counter began to click from the radioactive sodium which was absorbed into the blood stream and then circulated all the way to the fingertips. It was a very interesting demonstration of the use of tracers in biology. Well as a result of some of this, I made casual acquaintance with E.O. Lawrence and some others on the staff. I was able to get some radioactive tracer material by taking the targets which held their main experiments and there was always a little stray radiation hitting the targets. I was able to get the targets which contained radioactive iron, and cobalt, and manganese and I was I able then to do elementary experiments in the use of radioactive tracers involving iron, chromium, and manganese. At that time I used the Lauritsen Electroscope instead of the Geiger counter because the Geiger counter was still in the very elementary stages. But the Lauritsen Electroscope, which was a modification of the gold leaf electroscope that Madame Curie had used way back in about 1905, and this was a special one with an optical scale back in it, which made the readings easier, but the principle was actually the same. I have spoken to Dr. Glenn Seaborg and he used the Lauritsen. More recently I have talked to Phil Abelson and he used the Lauritsen electroscope. So these very simple, cheap devices can be used for very fine research work. One of the things that I tried to do at that time was to use the radioactive tracer chromium as an analytical tool for the determination of sulfate in very low concentrations. This, I was unable to do satisfactorily because of the very low level of chromium activity that I was able to get. Over 15 years later when radioactive chromium became available I did go into the laboratory when I was director of the Oak Ridge National Laboratory and finish up that experiment and actually published the results using chromium as a method for determination of the sulfates. It was sort of a trivial thing, but I did this more or less to satisfy my ego perhaps.
Well at any rate, as a result of this experiment that I was doing at the College of the Pacific and I did have some very fine students there, and I enjoyed the work very well, very much, but historical events did overtake us. I can remember distinctly, of course, one of the things beginning in about 1938 was the peace movement on the campuses of all of the colleges in the country. Our particular college was no different. We had a very powerful peace movement. The students were very enthusiastic about it at the time; of course Hitler was becoming more and more powerful, more and more threatening. You could see the war clouds gathering in Europe and this was, alarmed everyone and everyone was very anxious to preserve peace. But of course, those of us who had studied history could see that the peace movements were not going to be able to stop Hitler. At any rate, I can distinctly remember the leader of the peace movement who happened to be one of the students that I served as an advisor. Each one of us were assigned a certain number of students to advise on courses and sign approvals to take courses and so on, and he explained with great earnestness the demonstration that they were organizing, this was in 1938, as to the world wide peace movement. It was actually to be held at this football stadium there at the college. They had one of the high bishops of the church to serve as the main speaker and the students were all organized to give demonstrations with banners and so forth against war. It was a marvelous demonstration that they put on. It was very sad therefore, that just a few years later, as, within a course of a few months, war broke out in Europe and then later on, of course, we did have the bombing of Pearl Harbor. Oddly enough those students who were so active and so earnest in the peace movement overnight became very patriotic and were the first ones to volunteer to fight for our country. So I think there is a very good illustration about how history repeats itself because in England we had the same thing happen. I can remember talking to some people who had equivalent experience with the earnest students who were in the peace movement at Oxford and Cambridge, were among the first to volunteer for flying in the RAF and were perhaps the leaders in the great fight in the Battle of Britain. But to come back to as soon as the war broke out, things were changed entirely. The college was converted very much to preliminary training for the Air Force which was being expanded at the time and we were all asked to beef up our courses. I taught modified math courses for students going into the Air Force and, as I say, things were beginning to completely change around.
Actually a few years earlier, in my classes, there was an event which took place which was very significant. I believe it was in early 1939 that we had our courses in chemistry and one of our most popular activities was a Monday afternoon seminar in which we would take one given topic and assign it to a student and he would read up on it and then report on recent advances. Then we would cover all of the topics of immediate interest in the field of chemistry. This one day, there came out this report from Germany about the work of [Otto] Hahn and [Fritz] Strassman on the discovery that with the absorption of neutrons that uranium was split approximately in half giving rise to radioisotopes. This was a nuclear reaction which had not even been dreamed of, which had never occurred to people that it could possibly be. In fact the neutrons had been used to bombard uranium in many of the most prominent laboratories of the world: Fermi in Rome, the Curies in Paris, Hahn and Strassman in Germany, and in the United States there were several laboratories. All of them bombarded uranium, but none of them recognized the fact that in a large number of the hits of uranium, of neutrons on uranium, that there was a splitting of the atom. Almost all of them thought that the uranium was absorbing the neutron and becoming instead of uranium-238 it would become uranium-239 which would actually become then a transuranic. In fact, Fermi had postulated the existence of several isotopes of elements 93 and perhaps 94. By mistake he had actually been awarded the Nobel Prize in physics, I believe it was in 1937 or 1938, because of a mistaken diagnosis of what was happening. Of course, his tremendous work in the field of physics and then actually his methods, the development of the methods that he used full, he fully deserved the Nobel Prize for many other things besides that, but it was really interesting that he was mistaken in his interpretation. Well, as soon as that was published, in our little group of our chemistry seminars, we had some sort of a topic involved with something like ion exchange resins which were beginning to be made at that time. We discarded that topic and we discussed the implications of the splitting of the atom, whereas people had postulated that they could tap the energy of the atom eventually and give us an unlimited supply. This was the first time that we were actually able to postulate a practical way in which the energy of the atom could be tapped.
Well, later on, we find that, I found that when the war broke out, as things changed, and I received a call from Berkeley to come down and be interviewed for some new project that was being mobilized there. E.O. Lawrence was mounting this very secret project. In fact I really didn’t know what I was being called down there for until I actually joined the project. During the interview, I was given no hint what-so-ever as to what the project was. There was only that the project was extremely important and that it would be vital to the war effort and that my particular work would fit in very well to the project. So I decided to resign, or take a leave of absence in 1942 and join the project at the University of California.
[Break in video]
MR. LARSON: All right. Well now, with regard to joining the project at Berkeley, my first job there after receiving some slight indoctrination, at which time I was told what the project was. I can remember very distinctly in talking to E.O. Lawrence about the time schedule. He said it is absolutely necessary that the project be finished by July 1945 and it would be necessary to have roughly 100 kilograms of the product produced by that particular time. Now, this doesn’t seem like very much, but this was in July of 1942 and the process by which this U-235 was to be produced was the electromagnetic process which essentially was a large mass spectrograph in which the atoms of uranium were vaporized, ionized in an arc, accelerated and then bent in a magnetic field and at the end of 180 degrees travel would be collected in two separate small boxes, one containing, in theory, the U-235 and the other box the U-238. At the time, I joined the project in 1942, there had been produced somewhat on the order of a milligram or two of the U-235 fraction. So you can see there was a long way to go in order to get this produced.
Well, my first job was to distill the uranium tetrachloride which was the charge material for this process and to distill it and sublime it in a pure form so that it then could be used to, put in the source to be ionized. This was no mean job because it involved distilling under high vacuum and under carefully controlled temperature conditions and it was a very difficult process. It had to be done under absolutely vacuum tight preparation for the actual distillation and following that the unloading had to be done inside a dry box to avoid any possibility of moisture because moisture hydrolyzed the highly hydroscopic UCL-4 and then would destroy its usefulness. Well, we managed to get enough of this prepared and actually worked out a method for preparing it on reasonably large scale. So my next project was to turn our attention to methods for recycling the uranium in the process. It turns out that whereas the process sounds very simple, in practice, it’s not very simple. Uranium tetrachloride is vaporized and then is ionized in an arc and then led into the collectors containing, theoretically, the U-235 or the U-238. Unfortunately the ionization is very, very incomplete and so only five to ten percent of the uranium which is vaporized gets into the ionic stream and then the rest of it collects on the walls of the containers. So that had to be washed down thoroughly and collected because uranium was very valuable and then it had to be precipitated, recovered as uranium oxide and then converted to uranium tetrachloride, purified again and then go through the whole cycle again. So this got to be very complicated and there was a great premium on getting as high a recovery as possible because uranium was reasonably scarce, at least there was none to be wasted and therefore this had to be done with great care.
Well, we worked out a passable method for doing this and the recycling turned out to be practical. We did some of these experiments in the 37-inch cyclotron at Berkeley and tested our methods for recovery and worked it out on a small cyclotron which was converted into a mass spectrograph and we had a good research tool to carry out all of our experiments. Well this went on and the method which was being used was not all that satisfactory because in theory if you have pure uranium salts this works out very well, but uranium tetrachloride is a very corrosive material and any metal that it comes in contact with is immediately corroded and actually dissolves the iron and the steel. If there is stainless steel, it would dissolve some of the chromium off. If there are nickel parts, it would dissolve some of the nickel, so in general you ended up with a small amount of uranium of and a large amount of impurities to be recycled. This complicated the actual process considerably, in fact, lead to great difficulty as we will see a little later in the actual process. While this was going on, it seemed to me that the ideal thing to do instead of trying to separate out by certain agents the iron, chromium, nickel, and all the rest of these things and then leaving the uranium in solution that it would be much better to do it the other way around, precipitate out the uranium and then leave the rest of the things in solution. This was a good idea, but there was no agent known which would precipitate out uranium away from everything else, except one agent which is hydrogen peroxide. It turns out that uranium is precipitated by hydrogen peroxide to form uranium peroxide almost quantitatively under the right conditions and so it seemed that we had actually discovered the best possible way to do this. One complication however was that peroxide is very unstable in the presence of certain metals, particularly iron. In fact, iron actually decomposes the peroxide catalytically. For those of you who remember the early days of medicine, we used hydrogen peroxide to sterilize cuts and you had the impression that the hydrogen peroxide was working because it bubbled and fizzed. Actually this was because of the presence of certain enzymes in the blood and perhaps some iron which decomposes peroxide immediately. So in our so solutions, we had a lot of iron in them, there was no possibility of using this reaction because the iron catalytically decomposed the peroxide. This puzzled me a lot and I decided to eliminate the iron by complexing it with certain agents. There were complexing agents which would tie up the iron and make it unavailable for catalytic purposes and this, there was such a variety, I could, some of which are even used today in certain processes, but the net effect was they were all very expensive, all very scarce, and they didn’t work too well anyhow. So I finally had to abandon that approach and it was assumed that we really couldn’t do it until I hit on an idea which was probably a throwback to some of the research work that I did at one time. In my research work on biological compounds, I found that many of the organic compounds were unstable particularly if heated slightly. Even in some solutions they were unstable and so we had to keep them cooled. Many of these reactions where you separate important compounds of this type have to be carried out either in a refrigerated atmosphere, or carried out in such a way, so fast that you don’t, you didn’t get a chance to get this decomposition. So I tried the simple expedient of refrigerating the solutions and much to my amazement, the problem was solved almost immediately. If you kept the solution refrigerated, there was no decomposition. So therefore, at once, we had a possibility of precipitating the uranium out in very pure form, away from all of the other elements of the periodic table, because it was specific, peroxide precipitation was thought to be specific only for uranium. Well this was a little too good to be true. Actually it turned out later that the rare earths are also precipitated by peroxide and other things such as many of the transuranics, but since we didn’t have transuranics at that time, we didn’t have to worry about them. So for all practical purposes uranium peroxide precipitation was very specific and it worked for this particular purpose.
[Break in video]
MR. LARSON: The question then arose as to what are the quantitative relationships which will enable us to actually optimize the completeness of precipitation of the uranium peroxide and the variables, of course, are hydrogen ion or pH, the other variable is the concentration of the peroxide. There is a mathematical relationship between those called the equilibrium constant and I decided to determine the value of this so that we could use this in our calculations. With a simple series of test tube experiments, I worked out, by using I think about 20 test tubes and observing the effect in each one, to be able to zero in on the approximate values of the pH and the hydrogen peroxide concentration and then develop a mathematical relationship which enabled us to calculate over broadened number of conditions and we were able then to optimize the process for the proper conditions. A few years later, the equilibrium constant was determined with great accuracy and it turned out to be within one percent of that value that I determined by that rough method during a period of one day. So now we were essentially ready with the basic experiments and we were then ready to go to Oak Ridge.
Oak Ridge in the meantime had been selected as the actual locality for carrying out the production of the U-235. Oak Ridge, Tennessee, was located in the hills of East Tennessee. There were two small towns located on the site, probably as many as 25 people in one town and 30 or 40 people in the other, so there was no great upheaval of the locality. It turned out to be a very fine locality and was selected there for the production of U-235 by the electromagnetic method. Also it was selected for the site over another valley for the gaseous diffusion method of separating U-235 isotopes and then also as the pilot plant for the determination of the proper conditions for the separation of plutonium, which as carried out on the full scale at Hanford, Washington.
At that time, the projects were very highly compartmentalized. I was given a very high classification with regard to the amount of information available to us. Incidentally, on our badges there was a Roman numeral system whereby you could immediately tell what level of detail of technical consultation you could carry out. The lowest level of course was for the work men around the plant who had nothing to do with the process, involved in the pipefitting and the manual labor. Then there was a category two for some of the operators, and a category three which was for the supervisors and then a category four, which was for more detailed information and the top category for the executive people and I was, I had available category four, which after a period of a few months was raised to category five.
So I had all of the material that was necessary to carry out all of the work at the electromagnetic plant. But there was a category higher than that which was reserved to only a few people who had access to all of the information that was going on in all of the products, in gaseous diffusion product, process, and the thermal diffusion process, and the uranium-plutonium reactor process at Hanford, but that was limited to only a few people. There were a fair number of us who managed to guess a little bit about what was going on through rumor and a few other things. But the security was quite remarkable. In spite of the fact that many people knew, afterwards, knew all of what was going on, in actual experience there were very few of us, including myself, I did not know very much about the details of the other processes. More particularly, I didn’t know what stage they had reached except that I knew, for instance, when the reactors went into operation at Hanford, I received word through more or less rumor that the temperature of the Columbia River was being raised. So you could tell immediately that the project had reached a very high powered stage. But we were worried primarily about getting the electromagnetic process underway.
My particular responsibility was concerned with the chemical process and at first I was given the title of Director of the Technical Staff for Chemical Processes. That meant that I was responsible for seeing that everything that had to do with chemistry was going all right. From the start, almost nothing was going all right. As soon as the mass spectrographs went into operation, these were tremendous magnets which were wound in a circular pattern, more or less resembling a race track and there was a matter of about a hundred of these individual mass spectrographs, enormous things, about five to six feet in radius, about 10 feet in diameter. These, each one of these had a source and a method of ionizing the uranium, accelerating the uranium until it went into an orbit and collectors were placed to collect the U-235 at the 180 degree point.
My first job was to see that the U-235 was dissolved out of the collectors and this now turned out to be enriched material which was enriched from seven tenths percent U-235 to 15 percent U-235. Since the amount of enrichment that was necessary was something like 80 to 90 percent, it was necessary to take that enriched material and put it through again. We called that first stage through alpha and we called the second stage through beta. But the first complication that we ran into was that when we performed the original experiments out at Berkeley and we had all the best chemists there that we could get. I can remember one of the very fine chemists who was actually the discoverer of carbon-14. He placed a stainless steel piece right where the U-235 was to be collected and then after a certain number of hours, the U-235 was collected on this stainless steel piece. Then we took it, and I remember showing the experiment, poured nitric acid over this stainless steel piece and the U-235 which was collected on the stainless piece dissolved magically away. So from that simple experiment it was assumed that the U-235 could be easily arranged with, be dissolved with nitric acid and then purified from that point. It turned out when we went into production, the energy of the uranium ions was greater than that of the experiment. Therefore the uranium ions actually imbedded into the stainless steel. So when we came to dissolve it out, less than 50 percent of the uranium-235 dissolved out. The rest remained buried inside the stainless steel. You can imagine the panic that ensued then.
I had seen this trouble coming from almost the first day. So, I tried to think of a way we could get around this, and thought back to my experience as an electrochemist as a graduate student. I thought well if we, since the stainless steel doesn’t dissolve in nitric acid, we can’t get the uranium practically that way. The other heroic methods would have contaminated essentially dissolved the collectors completely, and that was not practical. So I thought of the idea of coating the U-235 collector box with metallic copper and we did that by electroplating it. Then, when the uranium buried itself into the metal, it buried itself inside the copper plate, and then all you had to do was dissolve all the copper outside with nitric acid. Copper dissolves very easily with nitric acid, and left the stainless steel in the metal below untouched. Then all we had to do was recover the uranium-235 from the copper. Now, this turns out to be a little difficult because there was over 1,000 times as much copper in solution as there was uranium. No matter how good your separations are, that does pose a problem. But it turns out that the large amount of copper was actually a help because the ether extraction from a saturated solution of copper nitrate and uranium extracts at more or less quantitatively the uranium into the ether layer. The ether layer can be easily stripped of the uranium and you get pure uranium. So actually we had to devise uranium extraction method almost right as we were doing this, as we were in the process.
I can remember the first experiments were we tried this out, ether being a rather explosive and catches on fire easily. I remember carrying out the experiments and we would keep one man there with the carbon dioxide fire extinguisher and we had to evaporate some of these things, so we had a hot plate. We ran into small fires probably every half hour or so, but they were easily put out. The only thing is every time we used a fire extinguisher, there was a procedure whereby you had to write up a report, so that it was more trouble writing up the reports than it was carrying out the experiments actually. At any rate, we later found out that other solvents other than ether, are even better than ether. So we managed to solve the problem of getting the U-235 out and instead of only getting about 50 percent out, we got about 98 percent, which was, we would like to have done a little better, but was satisfactory.
So we then were piling up enough of the 15 percent uranium to make this so-called Beta process possible. When you came to the Beta process, by now the material had gotten to be very valuable, up like a factor of 100 to 1,000, so you just couldn’t afford to lose any of that valuable material. You wanted to get at least 99 percent plus. There had been a method worked out for the precipitation and recovery of the uranium because again, you had to go through the same thing. You had to work the uranium which now was very valuable, 15 percent uranium in uranium tetrachloride quantitatively. That was worked out all right. Then it had to be ionized and separated again. Now when you collected it into the proper pocket, it was 80 to 90 percent enriched uranium which was suitable for the bomb project for defense purposes. So we were now on our way to actually collecting material which could be used as a weapon. Now the problem was that the method for separating this out was not as good as it should be and again the recovery was regarded as, the low recovery was regarded as actually, potentially disastrous. It would mean that the whole process would fail unless we could do better. In the meantime, as I mentioned before, I worked out the basic chemistry of the direct peroxide precipitation and that’s where the direct process peroxide precipitation was brought into play. When it was found out that we needed this, we had to junk all of the rest of the processing equipment and in order to, since uranium peroxide does not filter well, we had to separate it with centrifuges. So we immediately got the high priority order for getting all of the centrifuges that the Sharples Company put out diverted to Oak Ridge and actually flown in on bombers so that we could install it in the so-called Beta chemistry process and we, it finally worked.
MRS. LARSON: How many centrifuges were there that you had to bring in?
MR. LARSON: The number of centrifuges we had to bring in was not all that great.
We had a number, probably about 300 centrifuges all together, because they could be used not continuously, but they could be run and then emptied and then run again. So it worked out quite well. It did require a lot of labor, but with material at that point being worth nominally, we figured $1,000 a gram, it was well worth it to put in all the labor and all the equipment that was necessary. Of course at that particular point, the volume of it was not all that great. Remember we had to produce only 100 kilograms of this in total. So that process really worked out very well.
I did have quite a controversy because people were very loathed to abandon the old processes despite the fact that it wasn’t working that well. So, I had to enlist some rather influential friends in order to make the decision go the right way. The British representative, who was a vice president for research for Imperial Chemicals of England, was there. He was a very outstanding chemist and chemical engineer. He saw immediately that the process that I recommended would be the best one to work. Then also Dr. [Charles] Krause who was former president of the American Chemical Society, very prominent chemist, he also reviewed it and said that this was the only process that would enable us to get it going. This required…
MRS. LARSON: This was the only way to get the material away from the box?
MR. LARSON: This was the only way that the recycle of that very valuable Beta material could be accomplished. This was then christened, not by me, but by the plant manager who was delighted to see this problem solved. He actually named it the Larson Process. It really was a source of delight to see that process finally work and deliver, made certain that the whole process would not come to a grinding halt because of so much material being lost or held up during the recycle. So there was a constant supply of this 15 percent material being made available to the calutron, so that what was collected in the box, the 80 to 90 percent material could then be actually turned into the bomb material which was made available then, of course, to Los Alamos for the construction of the Hiroshima bomb.
Well, this, there were a lot of other small problems along the line, but most of them worked all right. As the time went along, there were many problems over on the side of the magnets and the sources and the receivers over on the, you might say, the physics side. They had their problems, but they were worked out also at the same time. For a while it looked like the magnets would fail entirely because they kept shorting out because there was metallic impurities left by the careless welders. It looked like the whole plan would have to be shut down. But they managed to pump oil through these big coils and get all of the metallic particles which were shorting it out removed in the, by filtering them out. Incidentally, those coils which went to make up the electromagnets were wound with silver rather than copper because there was a shortage of copper during the war and also silver was a much better conductor. It turns out that there was something like about, I believe it was something like over a billion, no the figure was actually 600 million ounces of silver were used in winding the coils for the electro magnets in the Y-12 electromagnetic plant. Later on when silver got to be $10 a pound and even higher, I reflected that there were over $6 billion worth of silver in those coils.
MRS. LARSON: Could you tell us the story about how that came to Oak Ridge? How the silver was obtained?
MR. LARSON: The silver was obtained by virtue of the fact that, as I say, there was not enough copper available for these big coils and Fort Knox had all of the silver and it was just sitting there. So there was, the Army Corps of Engineers just requisitioned the silver much to the astonishment and dismay of the people at Fort Knox, but it was ordered and delivered in the proper form for winding the coils. Incidentally this was not in the form of wire because those coils were, looked more like straps, one inch wide and perhaps an eighth inch think as I remember. As a matter of fact more than that, probably a half inch thick. I remember seeing all of this silver when it was removed from these electro magnets piled up in one room, seeing hundreds of millions of dollars’ worth of silver in one room over there. Later on, I was responsible for getting that silver back to Fort Knox and that was done with some work, but not too much of a problem.
MRS. LARSON: Wasn’t it true, excuse me for interrupting, it seems to me that when the silver arrived in Oak Ridge, it was quite an occasion and all you scientists began to stay up overnight and there was a whole weekend when no one saw any man involved in that problem because you were all down winding coils, or doing something about the magnet because the silver had come.
MR. LARSON: That’s, I think that particular story is a little, a little bit mixed up because the actual winding was done outside of Oak Ridge, and then shipped in in these great big magnet boxes. But the big excitement was that when they started to be tested and they were shorted out, people worked 24 hours a day, seven days a week trying to get the shorted material out. The only time it really came to view was when we cut them apart to remove the silver. Then it was viewed for the first time in Oak Ridge. But…
MRS. LARSON: How long after was that?
MR. LARSON: That was about two years, two to three years after the war was over. But there was no silver lost as actually it probably was far more secure at Oak Ridge than it ever was before or since at Fort Knox. In theory it’s possible to rob Fort Knox, but it was never possible to take one of those great big magnetic cases and cut them apart outside of an invasion by an Army. But at any rate there were a lot of problems to be unraveled and perhaps you could go on for…
MRS. LARSON: Well, I would like to interrupt one more time on that magnet story which I think is so dramatic and ask you did the treasury deliver the silver to you in the form of those straps that were…
MR. LARSON: No, the silver was delivered actually to the manufacturer of the great big electromagnetic boxes and…
MRS. LARSON: Who was that? Is it possible to say?
MR. LARSON: This was Alice Chambers in the case of the Alphas and Westinghouse in the case of the Betas. Those…
MRS. LARSON: They fashioned the…
MR. LARSON: They fashioned it. They had to take the ingots and fashion them into the proper size and so on.
MRS. LARSON: Straps which were then wound.
MR. LARSON: Straps which were then wound in the proper way to make the electromagnets. As I say it wasn’t rather dramatic that there was that much silver tied up for that purpose, but…
MRS. LARSON: It was the entire treasury of the United States.
MR. LARSON: It was literally probably 98 percent of all of the available silver in the United States, put in there for that particular purpose, but since it was just being stored, it performed a useful purpose, other than just sitting there during the war.
MRS. LARSON: You’re so modest. Do you think that today something like that could be accomplished even.
MR. LARSON: Well, certainly not in peace time. In order to get something like that done, the, probably it might take essentially years to unravel the red tape for such a transaction. Where as in those days, of course, there was, and rightly so, there was nothing that was needed for the war effort that was left undone. Fortunately the Manhattan Project had the top priority of all of the projects, much to the disgust of the Naval and Army and Air Force projects which were under way.
MRS. LARSON: Well couldn’t it also be said to the credit of the Manhattan Project, all that silver to the last half ounce was returned.
MR. LARSON: Well of course, later on I became superintendent of the Y-12 plant in 1948 and at that time we had the task of returning all of that silver and for all practical purposes, as close as you could weigh it, it was 100 percent. At least it was 99.99.
[Break in video]
MR. LARSON: Toward the end of June and the beginning of July, it was very apparent that we had a big effort being mounted in order to scrape together all of the U-235 that was available. There was no stone unturned to get every milligram of U-235 delivered to Los Alamos. It was about July 25 that General Groves came to Y-12 and we had about 20 to 25 of the key people involved meet together for lunch. General Groves was usually a very hard looking, hard driving individual with very little apparent sense of humor and no trace of humor in his eyes. However at this particular luncheon I have never seen a man in as good a spirits as General Groves. In fact looking at it in retrospect, I would say that his facial expressions on that day probably constituted a grave breach of security. It was obvious that he knew something that we did not know at the time. He, in his speech, indicated that we are now certain of the success of the project that we have now, which we had worked on for such a long time, never a hint of what caused great optimism on his part. Of course in retrospect we knew that it was a little over a week before they had exploded a bomb at Alamogordo and it was a complete success, where as he showed in his speech, no hint whatsoever of this particular event. All of us were puzzled at the enthusiasm which he showed. Of course, it was only about ten days later, it became abundantly clear to all of us why he was so happy that day. Well on August 5, we, of course, were working at our usual tasks in order to advance each one of the processes, refining everything, making sure that everything worked properly, ironing out bugs of course which continued to arise, and suddenly into my office, someone burst in and said, “They dropped the bomb.” I looked up and, of course, we had waited for this for a long time. My immediate instinctive reaction was to reply, “Did it go off?” Always in the back of our minds was the fact that there probably was no difficulty once you had U-235 in the proper quantities that you could make the chain reaction operate. What was concerning most of it, most of us, was the simple fact would it go off and fizzle so that there would really be no effect. Well the answer became abundantly clear in the announcements of President Truman which came on all of the radios, that the bomb was dropped on Hiroshima with the force of 20,000 tons of TNT and that, as a military weapon, the bomb was completely successful. Of course, about a week later, after leaflets were dropped and there was no positive indication that the Japanese were about to surrender, a second bomb was dropped on Nagasaki and, of course, practically immediately afterwards the Japanese surrender negotiations took place and hostilities ceased. This was a moment of great relief to all of us and we felt that our mission had been accomplished.
Well, after this had been accomplished, we began to review the things that we were doing and what meaning they had in light of the changed circumstances. It became very evident within a few months that the gaseous diffusion plant which had very limited production up to the last few weeks of the end of the war now began to produce material with great efficiency and great quantity and the so-called alpha units were immediately obsolete as compared to what could be done with the gaseous diffusion plant. Consequently within a few months, the alpha units were shut down and left the electromagnetic plant only with the task of taking the 12 to 14 enriched material from the gaseous diffusion plant and bringing it in the beta units up to the required bomb strength, or 80 to 90 percent. Of course after this, within a year the gaseous diffusion plant showed the ability to take the material all the way up to bomb strength material. It was then decided to shut down the plant, the beta units, and take over only that part of the operations which had to do with the conversion to the tetrachloride and a few miscellaneous things, and continue work on the research and development on the electromagnetic process in case certain improvements which would make it economical to continue.
Well, as far as the chemistry was concerned, which was my main responsibility, I decided that we should take a look at our whole operation and see what other purposes could be served by the skilled chemists that we had assembled there. As a result of several conferences which we had, we decided that there were three areas which could be actually worked on with great potential profit to the whole nuclear energy effort. One of them was the task of separating isotopes by chemical means. So we turned our attention to separating lithium-6 from lithium-7 because lithium-7 had a very low cross section and could therefore be used as a reactor coolant in the program which might eventually develop to use a reactor for electric power generating purposes.
Another possibility of great interest was the great skill which had been developed in the chemical research group in separation of materials which had really not been available previously. Since the group had acquired a great skill in solvent extraction the question was asked, “Are there better methods for the separation of uranium from the ores?” It became very evident that as the possibilities for the peaceful uses of atomic energy would develop, we would need tremendous quantities of uranium and those quantities would have to be from continually decreasing enrichment. In other words, when the first materials were, had come from the Belgian Congo or even from Canada, it was sometimes possible to get 10 and 20 percent ore and it became evident as we went to the United States sources, the content of uranium would be below one percent. So it was decided to investigate better methods for getting uranium out of these ores.
It soon became evident that there was a third very important problem so far as chemical separations were concerned and that is the need for highly purified zirconium. It turns out that in nature, zirconium is always contaminated with sister element, hafnium which is right below it in the periodic table. Hafnium is extremely difficult to separate from zirconium. In fact it had only been done on an experimental scale with great effort of fractional crystallization and literally hundreds of stages were necessary to purify the zirconium away from the hafnium. Now why is it necessary to separate the zirconium from hafnium? In order to use zirconium in a nuclear reactor, it must have the properties of having a very low cross section and not poison the reactor because of its absorption of neutrons and it turns out that all of the zirconium which was available had contamination by hafnium and was unsuitable. There is no more difficult separation in the whole periodic table than the separation of zirconium from hafnium and therefore it was an extremely expensive operation. In order to do this by fractional crystallization, the cost would be over $100 a pound.
Well, it was decided to use the modern techniques of solvent extraction which would be very much more selective in its ability to perform this separation. It was found that a thiocyanate complex of zirconium and hafnium made it possible to separate zirconium from hafnium by counter current extraction to a purity never before obtained and at a cost which was only one-one hundredth of the cost of fractional crystallization. This made possible the availability of zirconium for reactors and it was, the first use was made in the actual first submarine reactor, the Nautilus. I have here in my hand a small example of hafnium-free zirconium metal which was produced for the batches that went into the Nautilus fuel-element cladding and made possible the fine fuel elements that the Nautilus had. This was all done by the extraction method and all of it done in our research and development laboratories which produced all of the zirconium for the first nuclear submarine. So there was one triumph of new techniques of solvent extraction for the separation of very difficult materials.
The next important problem turned out to be a rather unusual one in that there never did develop a need for pure lithium-7, but for the weapons program, the, it became necessary to develop a method whereby lithium-6 could be delivered free from lithium-7 for purposes, for defense purposes. This was again thought to be very expensive, but it was found that a method whereby the counter current extraction again in a very special way, could be used. Actually using some of the techniques that we used during the war, it was possible to produce very adequate quantities of lithium-6 for defense purposes and there was a need for experimental reactors. A certain amount of lithium-7 was also produced by this particular method.
With regard to obtaining cheaper methods for getting uranium out of ores, again solvent extraction was very successful. At least at one time, almost 75 percent of the uranium which was produced in the world, used the solvent extraction method which was developed by this chemistry group in the electromagnetic plant. So starting from a conference held immediately after the war to determine the skills which this group could apply themselves to, three tremendously important projects were completed which had great economic significance to the old nuclear energy effort and great importance to the defense effort.
So this particular, at this particular time after the completion of some of these projects, I was asked to become director of the Oak Ridge National Laboratory, and in 1950, I assumed the responsibilities as director of the Oak Ridge National Laboratory. There, of course, I encountered a fantastic number of new problems. Dr. [Alvin] Weinberg, who was a research director, had organized a very fine program. Dr. [Eugene] Wigner who preceded him also started a number of very important programs. The Oak Ridge National Laboratory had the responsibility to help develop the so-called materials testing reactor which was a reactor which was designed to furnish a high flux of neutrons and consisted of fuel elements of aluminum and uranium, which in the proper configuration with water flowing through and so on, developed a very fine reactor for test purposes. The reactor was actually constructed in Idaho, much of the actual parts were done right at the Oak Ridge National Laboratory in our shops, and I made several trips to Idaho to help work with the Argonne National Laboratory group in actually finishing that reactor.
At the same time, there became evident the need for better methods for separating the fission products and plutonium and uranium. The original process as designed for the use at Hanford separated out the plutonium, but left the uranium and fission products together and they were both stored in big tanks out at the Hanford plant. Of course as the operations proceeded and plutonium was extracted from these, great quantities of uranium piled up in these tanks and there was a great economic incentive to develop a process which would separate out the plutonium and then also separate out the uranium and leaving the fission products by themselves. Well at that particular time, there was a compound discovered, trybutyl phosphate which with proper extraction agents would do a wonderful job of fitting into and separating out uranium away from plutonium and plutonium away from the fission products. So we had solved this particular problem and it was called the PUREX [plutonium-uranium redox extraction] process for plutonium-uranium extraction. This was actually put in at the Hanford plant for some of the processing. All of the processing at the Savannah River Plant which was constructed during this period used the PUREX plan and to this day throughout the world, the PUREX process slightly modified is still being used for the processing of spent fuel.
In addition to this, of course, the Oak Ridge National Laboratory participated in the project design to furnish a reactor which would be suitable for airplane propulsion. At that time, there was a concept which was developed using a molten salt which contained U-235 which circulated as a fluid fuel reactor. On the experimental scale it worked very well and in addition to that it showed great promise in a continually operating plant whereby the fuel reprocessing could be done more or less continuously. Unfortunately the project did not get very much attention from the industrial companies, but it was a great success as an experimental reactor which would accomplish that objective, if that objective ever appears to have validity in the future.
Another project of great interest at that time was the gas cooled reactor. There was very much pioneering work being done on the gas cooled reactor and subsequent reactors, which were built in Colorado and another one in Germany. It used much of the technology developed at the Oak Ridge National Laboratory at that time.
Perhaps one of the most interesting things that developed during that time was the participation of the Oak Ridge National Laboratory in the Atoms for Peace Conference. It was on December 8, 1953, that President Eisenhower delivered a speech at the United Nations offering to contribute both enriched uranium and scientific and technical knowhow for peaceful purposes. This caught the imagination of the world and subsequently a conference was arranged to be held in Geneva in July and August of 1955 and the entire world sent representatives to that conference. In addition to many of the exhibits involving radioisotopes, there was a very interesting exhibit which I think really made the success, exhibit-wise, of the whole conference. About six months before the conference was due to open, Dr. Tom Cole and Al Weinberg came to the office to discuss offering to actually construct a reactor and place it in position in Geneva to actually have an operating reactor right on site for the Atoms for Peace Conference. It sounded very daring and almost foolhardy at the time, and today of course it would be unthinkable. But in the short period of six months an operating reactor was constructed and all of the parts were put together in Oak Ridge and tested and placed on a plane for Geneva where we had a crew waiting to put the reactor together in a building which was designed and put up for the occasion just to emphasize the peaceful nature of the exhibit. It was placed in a building which had somewhat of a resemblance to a Swiss chalet. It was very efficiently designed building and served the purpose for housing the reactor and the accompanying exhibits very well and indeed was the hit of the conference. I can very well remember that Lewis Strauss who was then the Commissioner of the Atomic Energy Commission said that he had seen an awful lot of exhibits and a lot of exhibitions that were very wonderful, but were completed the week after the exhibit closed. He wanted nothing to do with such an exhibit. Consequently, we scheduled the construction and operation of that reactor practically down so that every hour was accounted for and nobody was allowed to fall behind in the design and construction of this reactor.
Well, there were literally dozens of other very outstanding programs that were carried out during the period of 1950 to ’55 and it probably was one of the most exciting periods of my life to actually go through and see the successful completion, some of which I observed in the test tube and then brought to fruition in multi-hundred million dollar projects that operated very successfully from the start.
[End of Interview]
PIONEERS IN SCIENCE AND TECHNOLOGY SERIES
ORAL HISTORY OF CLARENCE LARSON
Date Unknown
Transcribed by Jordan Reed
MR. LARSON: This is a test of lighting and exposure and it will be very interesting to see how this looks on the playback. First I am going to put on my coat and try that. All right and this will be the format of the recording which I plan to make now. What I am going to do is first start out with my primary interests at the end of graduate school in things that had to do with radioactivity following it up with my experiences at the College of the Pacific, now the University of the Pacific and with subsequent experience in being recruited for the radiation laboratory at the University of California which then lead to Oak Ridge and the exciting days there.
[Break in video]
MRS. LARSON: Okay, anything else you can think of I can buy…
MR. LARSON: Nothing more.
MRS. LARSON: Okay.
MR. LARSON: Fine. I am recording now.
MRS. LARSON: Oh, sorry.
MR. LARSON: So your voice is on there for posterity now. So this is a test to see if the audio is sufficient. I moved the camera back fairly far because this will give me more depth of focus on the subject and I think it will be much better if we can put the camera back further and then light accordingly. This will give us a more depth of focus on the subject and I think in general a much more pleasing appearance. The main thing of it is when we go back this far, is the audio still functioning. All right. We will try the test now.
[Break in video]
MR. LARSON: This next test is to determine whether or not I get better light distribution with a reflector over on the right hand side. I think just by visual inspection I don’t think that it makes all that much difference, but I think the only way we will be able to determine that is to watch carefully and analyze the playback to see whether it functions properly. I think we’ve got enough here now so that we can see if we made any improvement what-so-ever.
[Break in video]
[Dog barking]
MR. LARSON: Quiet, please.
[Dog barking]
MR. LARSON: This is the first test draft of the actual interview. My… cut. Cut.
[Dog barking]
MR. LARSON: All right. After that brief interruption caused by my good friend Prince, I will start this interview from scratch. Let’s take one. My story begins with some experiences I had in graduate school, which ultimately lead me into the Manhattan Project. We, as a graduate student, I did not work in radioactivity, but I did some research work on the role of electrochemical phenomena and physical-chemical phenomena and the relationship between inorganic compounds and organic compounds. So as a consequence, I did manage to get a fair understanding of the field of inorganic chemistry which was to play a very key role in my subsequent interests. My acquaintance with radioactivity and nuclear physics, of course, grew out of the fact that I was present at Berkeley, at graduate school during the exciting years when E.O. Lawrence was developing the cyclotron. I can remember distinctly attending one of our graduate science meetings when there was radioactive sodium produced in the cyclotron and a demonstration was made of the speed of absorption of sodium ions into the blood stream. In order to carry this out, a preparation was made containing radioactive sodium chloride and the subject drank this. Of course, it was a very low level, so there was absolutely no danger and then the Geiger counter was placed at the fingertips. It was really amazing. I think it was something like 35 seconds after drinking this that radioactivity began to appear in my, in the fingertips of the subject. So that was quiet a spectacular demonstration of the early uses of radio isotopes in the field of medicine. Of course, after the discovery of the neutron and after the discovery that artificial radioactive isotopes could be made by either bombarding neutrons, or by deuterons or by other suitable atomic projectiles, this was a very important and very active field of science immediately after 1935.
I can, very early memory remember the discussion of the discovery of artificial radioactivity and the sensation that it made during the years approximately, about, beginning in about 1935. Well, to make a long story short, almost immediately thereafter I took a position as professor of chemistry at the University of the Pacific, then called the College of the Pacific, where I spent five wonderful years as a teacher of inorganic and physical chemistry. During those years I maintained my interest in the spectacular field of radioactivity and I made arrangements with E.O. Lawrence to obtain some of the target material that was used to hold the particular element being irradiated. In other words, whenever someone wanted to carry out an experiment they put it in a holder and then the particular element was then bombarded with deuterons and then subsequently taken off the target to be worked up and the experiments carried out and the indemnification of the radioactivity made. Then, of course, there is sufficient stray deuterons that would hit the holder of the target and I was able to get some of the old targets which had of course iron, chromium and, I believe, some of the other, cobalt, and some of the other materials used to make stainless steel. So consequently, there was a slight amount of radioactivity which was generated as a result of the stray deuterons hitting these targets. Of course, the radioactivity was very small but adequate for experimental purposes. I think took these targets and dissolved them then using chemical separation methods. I was able to separate out several radioactive elements. At the time, of course, there was nothing new about these radio elements so I was not in a position to discover any new radioactive elements, but I was able to use the fact that we did have radioactivity to use in actual experiments to determine more efficient separation methods. In order to separate out, say iron, or cobalt, or manganese, or chromium from this mixture it was necessary to subject it to chemical methods, precipitate the different elements with different reagents and then actually get other methods developed, such as extraction and so forth, so that by doing this, I was able to sharpen my skills in the separation of one element from another, which was to play a real dominant part in my subsequent work on the Manhattan Project.
In order to do this of course you had to have a method for detecting radioactivity. As strange as it may seem, in those days, the Geiger counter had been invented long before that, but they were quite expensive and quite erratic and quite difficult to operate. However, Dr. Lauritsen of Cal Tech had invented a quartz fiber electroscope in which he used gold plated quartz fibers with those, electric charges placed on that. Of course the fibers would fly apart and then a scale was put in the back and this was put inside of an optical device so that you read it by looking in the view piece. Then by actually timing the decay of the radioisotope I was able to determine the relative activities. This was a very useful tool. In fact, I have talked to Glenn Seaborg quite recently and he mentioned to me, whereas most of the time he used the Geiger counter, he did find the Lauritsen electroscope a very useful tool, in fact almost superior to the Geiger counter at that time for certain purposes. This introduced me to radioisotopes and the actual ways in which you could use separation methods and it was a very fascinating field. In fact, one of the things that I did at that time was to develop a method for determining the amount of sulfate in very dilute solutions and by using radioactive chromium as a tracer, I was able to develop a rather crude method. About 15 years later, I went back in the laboratory, back in Oak Ridge, with modern techniques, modern apparatus, and I was able to develop this and actually wrote a short paper on the use of radioactive methods for the determination of sulfate. A rather non-significant contribution, but a very interesting one. The subsequent to that, of course, I was in coincident with that, I was very busy with my work as a professor and this kept me very well occupied. In fact, at that time, with really tight budgets, compared to budgets in colleges these days, we were expected to teach the equivalent of 15 lectures a week, of course, with the additional responsibility of running the examinations and tests and preparatory and laboratory work, so it did not leave me too much time for research work.
However, one of the things that I can remember in our teaching experience was that we would have a seminar every Monday afternoon to discuss recent findings in the field of chemistry and for this particular Monday afternoon I had read about the discovery of the Hahn and Strassman and the demonstration of the fissioning of the uranium atom. This was a very significant device. Here, in this one article, which did not occupy too significant a space in the journal, immediately all of those of us who could, were familiar with the field, and, this was worldwide, we could see immediately this was the key to unlocking the energy of the atom. Something that people knew could ultimately be done, but there was absolutely no progress in doing it in such a way that could be practical. All other attempts to unlock energy from the atom resulted in more energy being put into it than was, than you could get out of it. In this particular case, there were perhaps 100,000 or even an infinite amount of energy gained in the process of fission. So we spent that particular period actually discussing the implications of that new development in science.
At that particular time of course, the word fission was not used. I have a story somewhat later as to how the term fission originated. But this was very interesting and then, of course, within the next six months, articles appeared in the popular press as to the implications of this and speculation. But sure enough so far as scientific mention of this is concerned, this immediately dried up. No articles appeared in any of the journals and at first there was a self-imposed secrecy on the part of the scientists and, of course, later there was a government imposed secrecy there.
Well, as a result of the bombing of Pearl Harbor in December 1941, of course the nation geared up for war. Into our college, of course, we brought in courses of teaching fundamentals for development of aviators and the time was quite confusing. At the end of that term, I received a call from Berkeley to come down there to be interviewed for an important project. I must confess that until I actually appeared for the interview, I had no idea of what the project was. As a matter of fact, during the interview, the only reference was to a project of national importance and actually the word was used that the successful completion of this project would result in ending the war. So with that little information I decided to take a leave of absence from the College of the Pacific and arrived in Berkeley in June of 1942. There, of course, I soon learned what the project was all about. My first task in joining the project was to help out in preparing chemical compounds of uranium for use in the project. At that time, of course, we did not use the word uranium. The code word tubealloy was used instead. So that we never discussed any of the compounds or any of the results in any terms other than compounds of tubealloy and percentage composition of tubealloy and so forth and so on. For example if you wanted to refer to uranium dioxide, it was always tubealloy dioxide.
So another interesting thing was that the books containing the chemistry of uranium were actually removed from the shelves of the library. They were sequestered inside for the use of the project at the radiation laboratory at the University. One of my first jobs was probably pretty illegal, was to copy the reference book on the chemistry of uranium and I did this at home by using photographic methods. It proved, actually there was never a day that would go by where I didn’t refer to this reference work. It was absolutely essential to have all of the knowledge of the chemistry of uranium as we progressed.
Well this, my first job as I mentioned was to take uranium tetrachloride in an impure form and distill it. Now uranium tetrachloride is a solid material and it distills only at high temperature and perfect vacuum must be used. So we had heaters at the bottom of our vessel and then a cold, cooled spot at the top and then we would actually pump that down to, not a perfect vacuum, but a good vacuum, and start the distillation. Well this sounds a little easy, but this was my first experience in vacuum leak testing. That is a whole history in itself, but anyone who has done work in an evacuating apparatus knows that there are an infinite number of leaks that can take place and finding where those are really got to be quite a task. As a matter of fact, I was able to determine when I had plugged up the leak sometimes, but just listening to the vacuum pump and the change in the clicking of the vacuum pump determined whether or not you were making any progress. Of course, we had very refined gauges to determine the ultimate vacuum. I believe those were called McCloud gauges at that time. Since that time, of course, the art of leak detection has really advanced so that people have a very easy time of it these days.
Well, I was able to produce this uranium tetrachloride in a pure form and then we were, had to do this all in absolutely dry atmosphere because uranium tetrachloride is very hydroscopic. So we would do this inside a so-called glove box which is simply a box which is three feet by three feet by three feet with a glass front which holes cut into it and rubber gloves, sealed. You would place your material in there and then carry out whatever operations, either taking it out of the vessel where it had been distilled, or loading it into a vessel which is needed for subsequent operation.
The subsequent operation, of course, turned out to be that uranium tetrachloride was the material to use as a source material for the so-called calutron which was essentially a very large mass spectrometer. Now the mass spectrometer for those of you who don’t know it is a method by which you can separate isotopes into its component parts. Since uranium had two main isotopes, U-235 and U-238, you would place this uranium tetrachloride inside a vessel which in turn was in a magnetic field. Then the vapor from this was actually ionized and the uranium ions were sucked out by means of an accelerating electrode and they would go out into this space and be turned by the magnetic field. By the time it reached the 180 degree point, it was separated into two components, the U-235 component and the U-238 component. When I joined the project the most they had ever been able to separate up to that time was about one milligram of partially enriched U-235 and E.O. Lawrence told me that our objective was to make 80 kilograms of this material by July of 1945. Now this is three years, and up to that time, and this had to be relatively pure, up to that time we had one milligram of that. Well as you see, we had to make almost a billion times that amount in order to accomplish our objective.
So we set out and solved the problems of making the uranium tetrachloride and making it pure. I investigated then other methods for making the uranium tetrachloride. One method we had was to make uranium pentafluoride, which could be done by cooking uranium oxide in uranium, in carbon tetrachloride under pressure and heat and the conversion then resulted in uranium pertafluoride. Then, you had to take the uranium pentafluoride and actually separate it into uranium tetrachloride and uranium and some other compound. At first, it was thought all we did when we heated this was to drive off chlorine and so instead of having five chlorines you would end up with four. However, I found that if I were to do this carefully and distill it, there was a brown substance that was collected on part of the tube. This brown substance turned out to be uranium hexachloride. Now, people have postulated that uranium hexafluoride could exist, but the size of the chlorine molecule would make it impossible to make it fit six around the uranium molecule. I had quite a number of skeptics on this, but I finally proved the point and actually wrote up this as one of the discoveries of our group. I was very proud to have persisted in proving that this could exist. Soon after that we heard and this was kept very hush-hush except for very few people, that the project was promising enough and we went from a milligram, to 100 milligrams, to a gram and so forth. After about a year we were in the, almost in the kilogram state of the slightly enriched uranium. So we were confident at that point that we could scale up the process. Consequently the decision was made to go to a site in Tennessee which subsequently was called Oak Ridge in order to carry out the big industrial scale that was necessary to produce the quantities necessary for our war effort.
Well, one of the things that became obvious was that we needed two stages in order to carry this out. The first stage was to, would bring the uranium up to an enrichment of about 12 percent and 88 percent U-235 starting with less than one percent. Then you had to take that material and put it through again which would bring it up to 80 or 90 percent which was necessary to make a nuclear weapon. So we had, these two stages were called Alpha and Beta. As you can readily see, by the time the material got to be fed into the Beta stage, the material had got to be very, very expensive. So the, we looked at various and sundry problems along the way.
My first problem that vexed us was the fact that when the uranium traveled in these large vacuum chambers and was collected in a collector, in a stainless steel collector, it was found that the material had high enough energy that it buried itself into the stainless steel collector and it was impossible to dissolve it out by ordinary means. Now in our original experiments in Berkeley, we had put a stainless steel collector in a beam and collected some uranium. Then you took that stainless steel piece and used concentrated nitric and it dissolved off beautifully, however that was at considerably lower speeds. So when you got to the high energies in the production plant, that uranium just embedded itself inside the stainless steel and consequently only 30 to 50 percent of the material appeared as product.
This alarmed people very much, naturally and I, as soon as I saw this particular problem, I was fortunate enough to have on my staff a man who had considerable experience in electroplating in industry. I got the idea, the thing to do is to actually electroplate the uranium with the copper. Then copper, the uranium would go inside the copper, but copper dissolves very easily in nitric acid, so you could bring the uranium into solution without any trouble. So we worked out the method of doing this. We set up electroplating baths, actually using the industrial sinks which looked very much like laundry tubs, but we were able to do this in a very rapid form.
As a matter of fact, I can remember a conversation with E.O. Lawrence and I told him of my findings on this and he asked, I asked him, well, should we go ahead and of course he said, go ahead immediately. I said well, we’ll probably be able to put this into operation in about two weeks. He said, “I want every receiver that goes into these units electroplated by tomorrow morning.” We worked 24 hours around the clock. Sure enough, we were able to set up some lines so that we could feed some of these receivers in. We didn’t quite make the 48 hour deadline, the 24 hour deadline, but we were able to do this in about 48 hours. We completely changed the process in that short a time. Well, this gave rise to some other problems. However, at this time I think I’ll just stop here and see how this sounds so far.
[Break in video]
MR. LARSON: This is another test with additional lights. As a matter of fact I have added 150 watt flood light immediately above the subject so that I think we will get very much better and more even lighting with this. But there is no other way to find out but to test it. So I hope that this will, this additional lighting will show up in the proper way. If it works out we’ll have a much better set up as far as attempting to actually make documentaries of people in a more relaxed fashion. I think that also with this particular lighting, I think that it is much less obtrusive to the eye, but let’s see what it looks like. We may not like it at all. So at this time we’ll cut and rerun.
[End of Interview]